Heat the oven to 375°F. Lightly grease 8 cups of a standard muffin tin.
In a large bowl, combine the ground beef, egg, breadcrumbs, corn, red bell pepper, red onion, 2 tablespoons salsa, chili powder, cumin, salt, and black pepper. Mix gently until just combined.
Divide the mixture into 8 portions. Press half of each portion into the bottom of a prepared muffin cup, making a small hollow in the center. Place one mozzarella cube in each hollow.
Cover the mozzarella with the remaining meat mixture and pinch the edges together so the cheese is enclosed. Sprinkle the shredded Pepper Jack evenly over the tops.
Bake until the meatloaf muffins are cooked through and the cheese is melted and lightly browned, about 20 to 25 minutes. Let them rest in the pan for 5 minutes before lifting them out.
Sprinkle with chopped cilantro and serve with the remaining salsa.