Brown the ground meat in a skillet. When the meat is almost brown, add the onions, bell peppers, and garlic. Finish cooking the ground beef and then add the taco seasoning to the meat. Simmer and stir to combine before pouring into the crock pot casserole dish.
Top the taco meat with the drained can of corn. Then spread the shredded cheese over the corn.
Heat the mashed potatoes unitl they are soft enough to stir and stir in the sour cream. Top the casserole off with the mashed potatoes. Spread completely over the top of the casserole.