12 ouces 93%-lean ground beef
1/4 teaspoon freshly ground pepper
2 cups (about two) finely chopped portobello mushroom caps, gills removed
4 slices rye bread
3 tablespoons plain dry breadcrumbs
1 clove garlic, peeled
1 tablespoon Worcestershire sauce
8 teaspoons pickle relish
1 teaspoon chopped fresh thyme, or 1/2 teaspoon dried
4 (2 ounces) slices Swiss cheese
1/4 teaspoon salt
Position rack in upper third of oven; preheat broiler. Line a broiler pan with foil.
Gently mix beef, mushrooms, breadcrumbs, Worcestershire, thyme, salt and pepper in a medium bowl until combined. Shape into four patties and place on the prepared pan. Broil until cooked though, four to six minutes per side.
Meanwhile, toast bread. Rub each slice of toast with garlic.
Place one patty on each piece of toast, top each with two teaspoons relish and cover with a slice of cheese. Remove foil and place the sandwiches on the pan; broil until the cheese is just melted, 30 to 60 seconds.