Melt butter. Add green pepper and garlic. Cook until pepper is barely tender. Stir in flour and salt. Gradually add milk, stirring constantly, until thickened. Add spices and sugar. Stir in 1/2 cup grated cheese. Add the tomatoes, corn and onions and put into an 8-cup casserole. Sprinkle with the remaining 1/2 cup cheese. Bake, uncovered, for 50 minutes at 350°. (The casserole will thicken as it cools.)