1. Place the meat in a pot, cover it with water. Bring the pot to a boil, put a cover on it so the water doesn't all evaporate, and then set it to a gentle boil. Cook for about 40 minutes. (You can fry the beef for 5 minutes on each side instead).
2. Mix vinegar, sugar and salt in a deep plate. Slice the onion and put in the mixture. Let stand for about 15 minutes.
3. Cut beef, ham, cucumber and tomatoes into even thin strips.
4. Divide each ingredient in 2 or 3 parts (depending on the size of servings you want to get). Arrange 1 part of the ingredients on each serving plate (I arranged each ingredient to form a triangle).
5. It's best served chilled. Dress the salad with mayonnaise right before eating.