Combine the corn (1 can), bell pepper (¼ cup), mayonnaise (3 tablespoons), sugar (1 ½ teaspoon), salt (¼ teaspoon), and pepper (⅛ teaspoon) in a medium mixing bowl.
Melt the butter (1 tablespoon) over high in an 8-inch cast-iron or ovenproof skillet. Pour in the corn mixture and sauté just until warmed, 2 to 3 minutes.
Smooth out the mixture into an even, single layer, then sprinkle cheese (¾ to 1 cup) over top.
Turn on the broiler on high. Place the skillet on the top rack, closest to the broiler. Cook until the cheese melts and has golden brown spots, about 3-4 minutes. Watch closely so it doesn't burn.
Remove from oven and garnish with green onions. Serve while hot.