Boil the pasta according to package directions and drain it. Cut the tomatoes, using only the seedless flesh. The olives are cleaned of pits and cut into slices.
Prepare the salad dressing by mixing together the lemon juice, vinegar, olive oil, salt and sugar. In a large bowl, make a bed of lettuce.
Top with pasta, tomatoes, olives and crushed tuna fillet. Stir gently and pour the dressing on top.