Preheat oven to 375°.
Combine first 3 ingredients in a large bowl, stirring with a whisk until smooth. Stir in onion, bell pepper, whole-kernel corn, and cream-style corn; mix well. Add muffin mix and black pepper, stirring until well combined. Pour into an 11 x 7-inch baking dish coated with cooking spray. Bake at 375° for 50 minutes or until a wooden pick inserted in center comes out clean.