In separate bowls, combine all ingredients for each burger patty recipe. Make 6 patties per meat mixture using a 30 mL (2 tbsp) ice cream scoop. Flatten slightly with hands.
Preheat grill to high. Oil grate.
Grill patties for 3 to 4 minutes on each side or until they are well done. Season with salt and pepper.
Grill mushrooms evenly for about 3 to 4 minutes.
Garnish patties and mushrooms with cheese. Cook for about 1 additional minute. Keep warm.
Grill buns. Spread condiments inside the buns. Place patties and mushrooms on bottom buns. Garnish to taste with suggested ingredients and cover with top halves of buns.