Preheat oven to 350 F.
Heat the oil in small nonstick skillet over medium high heat. Add the corn, bell pepper and onion and sauté until translucent, about 5 minutes. Set aside to cool.
In a large bowl, combine the egg whites, oats, salsa, chipotle, 2 tbsp of ketchup, the beef, the cooked vegetables and a large pinch each of salt and pepper. Mix until well combined.
Using an ice cream scoop, divide the mixture into 12 lightly greased muffin tins. Top with the remaining 2 tbsp of ketchup using a brush and sprinkle with the cheese.
Bake for 25 minutes or until an instant read thermometer reads 160 F.
To freeze, remove them from the muffin tin by running a knife around the tin. Transfer to a tray lined with wax paper and cover with plastic wrap- refrigerate until cool. Place in the freezer for 1-2 hours or until frozen. Then you can transfer to a freezer bag that you label with the date.
When ready to eat, you can re-bake the muffins from frozen for 10-11 min at 425 F or pop in the microwave for a 1-2 min.