Grate on a fine grater:
¼ of a red onion, or less;
½ a clove of garlic, or less;
2 tomatoes, cut in halves, deseeded; just the flesh, holding them by the skin. Discard the skin;
Sprinklings of salt and pepper;
Generous slosh of olive oil;
Ditto of lemon juice.
Mix together well; taste.
Toss into vegetables, or serve wherever you would use tomato ketchup.