Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking dish with 1 tablespoon butter.
Combine whole kernel corn, creamed corn, corn muffin mix, sour cream, 1/2 cup butter, green bell pepper, red bell pepper, yellow onion, eggs, chili powder, and garlic salt together in a bowl. Pour into the prepared baking dish and spread evenly. Sprinkle 1 tablespoon paprika evenly on top.
Bake in the preheated oven for 35 minutes. Sprinkle Cheddar cheese and remaining paprika over the top; return to the oven and bake until cheese is bubbly, about 10 minutes more.