For tomato relish, blanch tomatoes (10-20 seconds), then refresh. Peel, finely chop, set aside. Meanwhile, heat oil in a large saucepan over medium heat, add onion and garlic, sauté until light golden and very soft (15 minutes). Add capsicum, chilli and spices, cook for 5 minutes, then add tomato, vinegar and sugar and season well to taste. Stir occasionally until very thick (25-30 minutes), then set aside to cool. Makes about 2 cups. Tomato relish will keep, refrigerated in an airtight container, for one week.
For buns, preheat oven to 250C. Combine yeast and 250ml lukewarm water in a large bowl and stand until foamy (5 minutes). Add flour and ½ tsp salt, mix until dough comes together, turn onto a lightly floured work surface, knead until smooth and elastic (5-10 minutes). Transfer to a lightly oiled bowl, cover with plastic wrap, set aside until doubled in size (30 minutes). Knock dough back, divide into 24 even pieces, roll each into a ball and place on two trays lined with baking paper. Cover with a tea towel, stand until doubled in size (15 minutes). Brush with eggwash and place first tray in oven, spray oven with a mist of water, cook until buns are golden (10 minutes). Repeat with remaining tray. Cool slightly, cut in half and place bases back on tray.
Meanwhile, combine minces, onion, egg and herbs in a bowl, season liberally to taste. Roll 24 golf-ball-sized patties, make an indent in the top of each, set aside on a tray. Heat half the oil in a frying pan, add half the patties, turn occasionally until golden and almost cooked through (5-7 minutes). Transfer patties, indent-side up, to bread bases, then repeat with remaining patties. Fill indent-side of patties with cheese and bake until melted and patties are just cooked through (3-5 minutes). Top each with a tomato slice, lettuce and tomato relish, sandwich with bun tops, secure with a toothpick and serve hot.