Cold Curried Shrimp

1/2 cup chopped onion
1/2 cup chopped apple
1 clove garlic, crushed
4 tablespoons butter
2 tablespoons flour
1 (16 ounce) can stewed tomatoes
2 teaspoons curry powder, or to taste
Salt and pepper
1 tablespoon mayonnaise
1 tablespoon lemon juice
3 pounds shrimp, cooked and cleaned

Saut