Marinate Mushrooms: In a bowl, whisk olive oil, balsamic vinegar, garlic, paprika, salt, and pepper. Brush this mixture onto both sides of the mushrooms. Let them marinate for 20 minutes.
Preheat Grill: Heat your grill or grill pan to medium-high.
Grill Mushrooms: Place mushrooms on the grill, gill side down. Cook for 4-5 minutes per side, until tender and lightly charred.
Prepare Buns and Toppings: Toast burger buns on the grill for 1-2 minutes. Layer lettuce, tomato, grilled mushrooms, and avocado slices on each bun.
Assemble and Serve: Add optional cheese and secure the top bun. Serve immediately with your favorite sides.
Notes
Substitute avocado with guacamole for an extra flavor boost.
Store leftover mushrooms in an airtight container for up to 2 days.