My mother always fixed this for us during the summer and for potluck dinners, and everyone always ate it up and would ask for more.
Ingredients
4 yellow squash, sliced
4 medium tomatoes, sliced
2 green onions, chopped
2 tablespoons red wine vinegar
2 tablespoons olive oil
1 tablespoon Dijon mustard
½ teaspoon salt
¼ teaspoon freshly ground black pepper
Directions