For my money the old Edmonds Cookbook tomato relish is one of the best. I've modified a few ingredients but essentially this is it.
• 1½kg of tomatoes (I used beefsteak)
• 2 medium red onions thinly sliced
1. Cut a small cross in the base of each tomato and blanch in boiling water to remove the skins.
2. Quarter the tomatoes, mix with the onions, sprinkle with 1½ teaspoons of salt. Leave overnight.
3. Drain off the salt the next day and put in a heavy-based pot.