1. Roughly chop portabella mushrooms and onion and place in the bowl of a food processor. Pulse several times, until minced.

2. In a large bowl, combine mushroom mixture with ground beef.  Add the Worcestershire sauce, cheese and a dash of salt and pepper.  Stir well to combine.

3. Cook burgers in a preheated pan or a on grill over medium high heat, about 10 minutes** (depending on thickness), flipping once. Top each with a slice of cheese, if desired, and cover pan until cheese melts.

4. Serve each burger on a bun, topped with arugula, red onion, tomato, and garlic aioli.

To make garlic aioli:  combine 1 clove of garlic, finely minced, with 4 tablespoons of mayonnaise.

**When burgers are cooked, they will have an internal temperature of 71°C (160°F) and will no longer be pink inside.