First, chop up mushrooms, diced. Heat oil in a small skillet set to medium heat. Add mushrooms and cook, stirring occasionally, until browned and liquid has evaporated, about 5 min.
Next, add 2 tbsp vinegar, garlic powder, and paprika; cook, stirring 2 minutes. Place in a bowl and let cool.
Toss sliced red onion in a bowl with remaining 2 tsp each of oil and vinegar and ¼ tsp salt.
Then, add beef or turkey and remaining ¼ tsp salt to mushroom mix. Mix well!
Stir in McCormicks seasoning and combine well. Form patties with hands and grill on preheated grill to desired temp. Grill red onions along with patties. Add cheese on top of meat until melted.
To form burgers, use whole wheat buns and top with burgers and sliced onions.