lbs. grass fed ground beef
1/4 cup diced onion
1 ripe avocado, mashed
1 egg
1 small sweet potato, cooked and mashed
garlic powder
black pepper 
smoked paprika
8 Portabello mushroom caps (as the bun)
iceburg lettuce
Preparation
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 
