Lemon could be added as a marinade or, depending on how cavalier he feels, he might knock up a soup with tom yum paste, coconut powder and desalinated water.
Whatever ends up on Giesen's menu, it is for a cause close to his heart.
He lost an aunt and two mates to suicide in recent years. The objective is to complete the Talisker Whisky Atlantic Challenge to raise $1 million in the name of mental health for the Bravehearts, Black Dog Institute and Victim Support charities. A sum of $13,862 has been secured so far under a campaign branded The Blue Rower.
Giesen knows eating on the voyage is less about Michelin-star meals and more about chowing down enough energy for his stints on the oars.
He cites the case of veteran long-distance rower Leven Brown - who's working as his mentor - being forced to open a bag of potato chips by sitting on them after battling to the point of exhaustion through a hurricane.
"Because I'm going solo, I can row or sleep as much as I want," Giesen says. "But I might break the day into six four-hour slots of three hours on, one hour off. So I'll need to eat so much food for fuel, then work out a sleep and rowing pattern around it."
Why go to such extremes?
"The answer is 'why not'?" he says. "I don't have an answer to why my aunty and two mates did that. In fact, it'll always be a demon question in the back of my mind, so while I'm still living and breathing, why not live life to the full."
Giesen says he has never officially suffered depression, but that should not stop Kiwis talking about it.
"I went through one spell where I'd wake up unhappy. I kept telling myself 'tomorrow will be better'.
"If I ever did have depression, the best way for me to deal with it would be through exercise, to control those inner thoughts.
"I needed to break the silence. I don't want to be that New Zealand man who won't talk about his feelings."
Giesen believes the next generation can change the way New Zealanders think about mental health.
"Some New Zealanders are still stuck in backward ways. Hopefully younger people can be open and talk about it like John Kirwan as an All Black. But who among the new generation will know him if they don't follow rugby?"
Giesen was once a surf lifesaver at Taylors Mistake, but never rowed competitively. He has been subjecting himself to three-hour rows on the ergometer to build his base fitness.
Brown told him his erg scores, with an average 2m 19s split for each 500m, mean his fitness is "as good as it can get" for the task at hand.
"I know I can do more, but I still expect to get broken out there.
"I'm hoping it helps that I can read surf to know when to stroke and maximise the power of the waves.
"I also completed my yacht masters course last year in the Canary Islands [including more than 5000 sailing hours] which helped me understand swells."
Planning has been key to building confidence for his expedition. Giesen has fixed and handheld GPS units onboard, alongside VHF units and charts to plot his daily position. He will eat dehydrated food, and has a water-maker and manual back-up which can pump out 28 and two litres an hour respectively.
Brown is helping Giesen with his weather navigation; a sound plan given he has rowed 30,000 nautical miles on various routes around the world.
As a result, Giesen will get five different chart options a day and take the advice of 2001 trans-Atlantic race winners Kevin Biggar and Jamie Fitzgerald. They got the weather in the morning and plotted incremental measures of achievement on their chart.
He will also take the pair's advice on oars.
"They used wetsuit material for hand grips because it takes the moisture away and softens up the catch [of the blade in the water].
"It's a bit squishy and better on your tendons. I've got an old wetsuit so I'll probably cut that into strips."
Eight boats will contest the event's solo class. Giesen's is one of the oldest in the fleet but it's "made with love" and "seamless finishings". He can put out a parachute anchor if Arma-geddon pops up in the middle of nowhere.
"My theory is 'don't touch it'," Giesen says of the chute. "I'm about 10 per cent of the boat's weight so I can manoeuvre it in the big surf."
Giesen finished a degree in viticulture and winemaking in 2015 and was working as a chartered skipper for Kiwi company MedSailors in Croatia on sailing holidays for 18-30 year-olds. Then he had an appetite for something new.
"It was good fun, a lot of drinking, but by the end I'd had enough. I wanted to focus on this."
If he's seeking inspiration, Kiwi Dame Naomi James embarked on a similar adventure 40 years ago, becoming the first woman to sail solo around the world via Cape Horn.
She began her circumnavigation on a loaned 53-foot yacht just over two years after learning to sail.
James suffered radio silence for 8000 miles heading south in the Atlantic, lost her kitten Boris overboard and was forced to stop over in Cape Town when her self-steering failed. Three months into the voyage, she realised she was miscalculating latitude with longitude on her distance chart.
The final paragraph of her 1979 autobiography, At One With The Sea, summed up what the achievement meant.
"In attempting this voyage I risked losing a life that had at last become fulfilling; but in carrying it out I experienced a second life, a life so separate and complete it appeared to have little relation to the old one that went before.
"I feel I am still much the same person now, but I know that the total accumulation of hours and days of this voyage have enriched my life immeasurably."
Giesen's endeavours should end up enriching other lives, too.
