Mix all together except mushrooms and lettuce. Shape into patties of desired size (to fit mushroom caps).
Grill patties until desired doneness (about 10 minutes per side on med-heat grill).
Grill mushroom caps for 3 -5 minutes.
Serve on a large leaf of iceburg lettuce, with the mushroom caps as the bun… and typical burger toppings of your choice 🙂
I served my burger with rutabaga fries and grilled peppers and zucchini… 🙂