Coat an 8 x 8-inch square cake pan with vegetable cooking spray. In medium nonstick saucepan, bring 3 cups water to a boil. Stir in grits and salt, reduce heat to low, cover, and simmer for 12 minutes. Meanwhile, place diced red pepper in bowl, cover, and microwave 2 minutes. When grits are cooked, stir in cheese, corn, and cooked pepper. Pour into prepared pan and smooth top with a spatula. Cover with plastic wrap and refrigerate until set, at least 3 hours; can be refrigerated up to 3 days.
Heat grill. Cut chilled grits into 9 squares. Coat with vegetable cooking spray, and grill over low heat until heated through.