All of these amounts are quite approximate. Just adjust to taste.
2 cups chopped tomatoes (I use grape or cherry tomatoes)
2 cups chopped cucumber
1/2 cup diced or crumbled feta cheese
1 tablespoon red wine vinegar
2 teaspoons olive oil
1/2 teaspoon dried oregano (or 1 tablespoon of fresh)
salt and pepper to taste
Toss all ingredients together and chill.