In bowl, combine beef, egg, breadcrumbs, onion, salt and pepper. Shape into 12 small patties, about 3 inches (8 cm) in diameter. Barbecue, broil or pan-fry in skillet until instant read digital thermometer reads 160°F (71°C), 3 to 4 minutes per side. Sandwich in bun, with desired topping.

Topping:

Place 1 bacon slice diced in a skillet over medium heat. Add 1-1/2 cups (375 mL) sliced Ontario Mushrooms; cook until tender, about 4 minutes. Season to taste with salt and pepper. Place 4 cooked burgers in buns, spread each with mustard and top with mushrooms and a slice of aged Ontario Cheddar, Brie or Swiss cheese.

Spread 1 tsp (5 mL) pesto on each of 4 cooked burgers. Place Ontario Greenhouse Lettuce Leaf on each bun bottom. Place burger on lettuce and top each with Ontario Greenhouse Tomato slice and a slice or two of Ontario Bocconcini cheese. If desired, grill or broil to melt cheese.

Brush 4 cooked burgers with 1 tsp (5 mL) teriyaki sauce, place in buns. Combine 1/4 cup (50 mL) each shredded Ontario Carrot, diced Ontario Greenhouse Cucumber and Ontario Bean Sprouts. Top burgers with vegetables.