In a large bowl, mix the first 4 ingredients (beef through thyme). Form beef mixture into 4 patties.
Brush mushroom caps with olive oil and season with sea salt and freshly ground black pepper to taste.
Place burgers and mushrooms on the grill. Close lid and cook burgers for 5 to 10 minutes on each side, until beef reaches preferred doneness. Cook mushrooms for 2 to 5 minutes on each side, until tender. Layer, 1 mushroom cap, spinach, burger, onion, avocado and second mushroom cap. Serve warm.
Notes
SERVING SUGGESTION: A big spinach salad tossed with Leanne’s Basic Vinaigrette.NUTRITION: 472 Calories; 35g Fat (63.8% calories from fat); 27g Protein; 17g Carbohydrate; 5g Dietary Fiber; 85mg Cholesterol; 106mg Sodium. Exchanges: 0 Grain (Starch); 3 Lean Meat; 2 ½ Vegetable; 0 Fruit; 5 Fat.