Veggie Salad

Ingredients

• 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 or margarine