Heat the broiler to high.
In a medium bowl, stir together the corn, red bell pepper, mayonnaise, sugar, salt and black pepper until well combined.
In an 8-inch cast-iron skillet over high heat, melt the butter. Add the corn mixture and sauté until warm, 2 to 3 minutes.
Spread the corn into an even layer and top with the shredded mozzarella.
Broil until the cheese is melted and starting to brown, about 4 minutes.
Garnish with the green onion and serve hot.
Leftovers can be stored in an airtight container in the refrigerator for up to 3 days.