Chop the tomatoes, cucumber and pepper and place in a bowl.
Drain the onions and add them to the rest of the vegetables.
Place the garlic in a mortar with a pinch of cumin and a pinch of salt and a few drops of olive oil until you have a paste. In another small bowl mix the rest of the olive oil, vinegar and salt, add the garlic paste and mix well.
Add the dressing to the salad and mix well. Cover and refrigerate.