Place frying pan on burner, and being to medium heat.

In mixing bowl, season beef with garlic powder, black pepper, and salt. Pack beef into square patty, and place in frying pan. Cook until internal temp reaches 155°F.

In small bowl, combine both mayonaisses and the dijon mustard. Whisk together, and spread evenly across tortilla.

Wash veggies. Cut slice of onion, core, and cut into thirds. Cut 2 slices of tomato. Cut 2 mushrooms into thick slices (4-5 slices each).

When beef patty is cooked, add cheese and cover. Cook until cheese is melted, remove from heat, and place in center of tortilla.

Leaving grease in pan, add butter. Turn heat to high, and add mushrooms and onions. Sautée until soft and fully cooked.

Place tomato slices on cheese, and add onions and mushrooms. Fold closed into a square.