Cut eggs in half lengthwise, remove yolks to a bowl. Mash yolks with the mayo, mustard, salt, and pepper.
Fill whites with yolk mixture, set deviled eggs aside.
Preheat your oven to 220° C (425°), get out a 7x11 inch baking pan.
Melt the 3 tablespoons of butter in a medium saucepan, whisk in the flour until smooth.
Stir in the tomatoes, onion, sugar, salt, and black pepper. Cook until thickened, stirring constantly.
Pour sauce into the baking pan.
Arrange the deviled eggs on the sauce.
In a bowl, mix together the bread crumbs and the 2 tablespoons of melted butter, sprinkle over the top of the casserole.
Bake for 10 minutes or until hot.
Serve over toast or buttered egg noodles, enjoy.