In a small skillet, over medium heat, cook bacon slices till done. Drain the
bacon on paper towels Add onion to bacon fat remaining in pan and cook until onion is
softened, but not darkened. Remove onion and place in a small sieve. Allow excess fat to
drain from the onion.
When bacon is drained, chop the slices and combine with the onion.
In a large mixing bowl, combine the ground beef, egg, chili sauce, salt
and pepper. Mix well but without overworking the meat. Add mushroom caps, cheese, and then bacon and onion
mixture. Mix again very lightly. When ingredients are well mixed, form into patties.
Prepare a medium-hot fire in a charcoal grill with a cover, or preheat a gas grill to medium-high. When the grill is ready, brush the grill rack with vegetable oil.
Cook patties on the hot grill to desired doneness, 4 - 5 minutes for medium.
Serve on lightly toasted hamburger buns slathered with Dijon Mayonnaise.