A picture of the deal, posted on Twitter, attracted widespread outrage as many pointed out that while sirloin steaks are expensive, cauliflowers can be bought for under $5 when in season, at most supermarkets.
Writer Jamie Klingler shared a pub board advertising the offer at The Queen's in Primrose Hill.
She tweeted: "£28 for two pieces of Cauliflower. That's mental. Like properly mental."
Her tweet spurred on hundreds of shocked and angered responses.
One Twitter user replied: "It's a MASSIVE profit spinner. I think the sign is actually taking the mic [out] of vegans."
Another wrote: "Restaurants now doing all they can to exploit vegans for as much as they can squeeze out of them. All for produce that costs pence. Unfettered capitalism and mass food commoditisation in full flow."
And another added: "This is one of the most infuriating things about being veggie/vegan! I understand that you have to pay for the chef, waiting staff and overheads but how in chipping tits can cauliflower cost the same as steak!"
The offer is running at all of Young's 148 pubs across London and the south east of England.
On Twitter, the chain defended the dish and said the vegetarian alternative was of "premium quality".
In response to a customer querying the cost difference, it replied: "Both dishes are of premium quality, the vegan dish is an alternative for those who do not eat meat.
"We also have other options available on our main menus."
Slicing a cauliflower and calling the result a "steak" has become a trend in recent years, and Marks and Spencer pulled theirs last year after there was widespread backlash over the 'excessive' plastic packaging and the inflated price.
The shop was criticised on social media after a shocked customer pointed out that their £2.50 ($5NZD) cauliflower "steaks" are simply sliced cauliflowers sold in excessive packaging. She commented that at her grocery store, one can buy a cauliflower for a little over 60 pence ($1.10NZD).