Prepare the sauce. Pour hot water and cheese into a small bowl, knead well with a fork, and then add the remaining ingredients for the sauce, stir well, cover and refrigerate.
Finely chop the eggs. In a small bowl, mix the cut eggs with 1/4 cup cheese sauce, season with salt and pepper to taste, and set the bowl aside.
Brush 8 out of 12 slices of bread with about 1/2 cup cheese sauce. Place the fried bacon on 4 greased slices of bread and top with the tomato rings.
On 4 dry slices of bread, put eggs and sauce, and top with salad leaves and onion rings. Place the last slices on the bacon and tomato slices. With the remaining 4 slices of bread greased with sauce, cover the egg sandwiches, sauce down. You can skewer the egg sandwiches with cherry tomato slices (if desired).