Chicken-Zucchini Casserole

1 small box Stove Top chicken dressing
2 pounds zucchini,  diced
1/4 diced cup onion
1 cup sour cream
1 (10 3/4 ounce) can cream of chicken soup
2 tablespoons butter, melted
1 pound hamburger
1 small can mushrooms, drained
8 ounces shredded Cheddar cheese

Brown hamburger and onion; drain well.

Mix all ingredients except cheese. Put into a greased 9 x 13-inch pan. Bake at 350 degrees F for 30 minutes.

Remove from oven, and place cheese on top; return to oven just until the cheese melts.