In a small bowl, add the dried porcini mushrooms and enough hot water to cover the mushrooms.
Let the mushrooms stand for about 15 minutes, or until softened.
Using a slotted spoon, transfer the softened mushrooms to a cutting board. Chop the softened mushrooms.
Off heat, coat a grill rack or large grill pan with nonstick cooking spray.
Preheat a gas grill or grill pan to medium-high heat, or prepare a medium-high fire in a charcoal grill.
Place 4 bacon slices in a single layer between paper towels. Microwave the bacon on High for about 30 seconds, or until partially cooked but still flexible. Drain the bacon on paper towels
Repeat with the remaining 4 bacon slices. and set aside.
In a large bowl, add the ground beef, cremini mushrooms, chopped porcini mushrooms, red onion, and ½ teaspoon kosher salt. Mix until combined.
Shape the mixture into 4 patties.
Season the patties with salt and black pepper.
Place 2 bacon strips in a crisscross pattern over each patty. Tuck the bacon ends underneath each patty.
Place the patties on the grill with the bacon side facing down. Grill for 6 minutes.
Turn the patties over. Grill for about 6 more minutes, or until the bacon is crisp and an instant-read thermometer inserted into the center of each patty reaches 160 degrees F.
Sprinkle a scant ¼ cup shredded cheese over each patty.
Close the grill lid. Cook for about 30 seconds, or until the cheese melts.
Sprinkle the tomato slices with the remaining ¼ teaspoon kosher salt.
Place each patty on the bottom half of a hamburger bun. Add 1 tomato slice, 1 lettuce leaf, sliced onion, and the top half of the bun.
Notes
Tips and Tricks
Chop the mushrooms small - Smaller pieces mix into the patties more evenly and help the burgers hold their shape.Partially cook the bacon - Microwave the bacon only until it is flexible. If it gets too crisp before grilling, it can break when wrapped over the patties.
Storing and Reheating
Store in the Refrigerator - Place leftover cooked patties in an airtight container. Refrigerate for up to 3 days. Store buns, lettuce, tomato, and onion separately.Reheat on Stovetop - Place a patty in a skillet over low heat. Warm until heated through.Reheat in Microwave - Place a patty on a microwave-safe plate. Cover with a paper towel and heat in short intervals until warm.Reheat on Grill Pan - Place the patty on a grill pan over low heat. Warm for a few minutes on each side.