Zucchini Cornbread Casserole

1 box (8.5 oz) corn muffin mix
2 medium zucchinis, grated
1 cup sour cream
1/2 cup melted butter
2 eggs
1 cup shredded cheddar cheese
1/4 cup chopped green onions
1/2 teaspoon salt
1/4 teaspoon black pepper