1. Preheat oven to 325°. Spread mayonnaise on one side of each slice of toast. Arrange toast, mayonnaise side up, in a greased 8-in. square baking dish. Top with cheese slices and bacon.
2. In a small saucepan, melt butter. Stir in flour, salt, and pepper until smooth. Gradually add milk. Bring to a boil; cook and stir 2 minutes or until thickened. Pour over bacon.
3. In a large skillet, fry eggs over medium heat until they reach desired doneness; place over bacon. Top with tomato slices; sprinkle with cheddar cheese and onions. Bake, uncovered, 10 minutes. Cut in squares; serve with lettuce.
