Preheat oven to 350°
Prepare baking sheet by covering with foil and spraying with a non-stick cooking spray. Using a biscuit or cookie cutter, take out center of each bread slice making a circle. Place bread on prepared pan. Brush melted butter generously over slices. In a medium sauté pan, sauté the chopped onion in the reserved bacon drippings. Add a pinch of salt and pepper. Once onion is translucent and a little brown around the edges, remove from the heat. Add the crumbled bacon and tomatoes to the onions and stir until just mixed. Set aside. Crack an egg and drop in the center of each piece of bread. Sprinkle with salt, pepper and Herbs de Provence. Place in oven and cook just until the egg whites are done. Remove from oven and top with the grated cheeses, dividing evenly among all four bread/egg slices. Put oven on broil and return slices to oven. Once cheese is bubbly remove from oven.
To Serve: Divide onion mixture evenly and spoon over each slice. Serve Hot. 'Slainte' (pronounced 'slawn-cha', meaning Health! The equivalent of Cheers!)