1 small onion, chopped
1 medium green pepper, chopped
1 medium yellow squash, chopped
1 medium red bell pepper, chopped
1 medium zucchini, sliced
1 8-oz pkg mushrooms, sliced
1 c olive oil
1/2 c balsamic vinegar
2 T butter

In saucepan melt butter and sauté vegetables lightly-don't overcook. Remove from heat and cool completely, transfer to bowl. Blend together oil and vinegar and pour over vegetables, salt and pepper to taste. Cover and refrigerate overnight.