In a bowl, mix ground beef with salt, pepper, and onion powder. Form into three equal-sized patties.
Heat a skillet over medium-high heat and cook the patties for 2-3 minutes per side, then reduce heat and cook for an additional 5 minutes until fully cooked. Set aside.
In a small bowl, mix mayonnaise, ketchup, bacon bits, sweet relish, and sugar to create the sauce.
Butter one side of each rye bread slice. Spread the sauce on the unbuttered side of three slices.
Place a slice of cheddar cheese and a slice of Provolone on each sauced bread slice. Add a cooked patty on top, then top with the remaining bread slices, buttered side facing out.
Wipe the skillet clean and heat over medium heat. Cook the sandwiches for 2-3 minutes per side until the bread is golden brown and the cheese is melted.
Slice and serve immediately.