Pasta stuffing shells

• butter or margarine • salt • water • garlic powder • pepper • 4 oz • medium zucchini, cut into 1/4 inch slices • fresh mushroom, sliced • large onion, cut into 8 wedges • medium carrots, scraped and cut into 1/4 inch pieces • medium size green peppers, cut into 1/2 inch pieces • medium size yellow squash, cut into 1/4 inch slices