In a large skillet, heat 2 tablespoons of extra virgin olive oil over medium heat. Add 1 chopped medium yellow onion and 1 cup of chopped white button mushrooms, then season with salt and pepper. Cook for 10-15 minutes, stirring occasionally, until the vegetables are softened and starting to caramelize.

In a mixing bowl, combine 1 pound of lean ground beef with 2 tablespoons of BBQ seasoning. Gently mix the ingredients until just combined.

Divide the ground beef mixture into equal portions, flatten each into a patty, create a small indentation, fill with the sautéed onions, mushrooms, and a slice of cheddar cheese, top with another patty, seal the edges.

Preheat your grill to medium heat, around 375°F (190°C). Grill the stuffed burgers for approximately 6 minutes on one side, flip and grill for another 5-6 minutes until the internal temperature reaches 160°F (71°C).

Transfer the burgers to a clean plate and allow them to rest for a few minutes. Prepare your buns and toppings, then assemble and enjoy!