Portobello Mushroom Burger Portobello Mushroom Burger Cheryl Santangelo Feb. 06, 2013 Comments Portobello Mushroom Burger Makes 1 burger. Recipe is from Cheryl Santangelo, of Red Hill Creole Mushroom Farm, Independence. Fresh Louisiana-grown portobello mushroom Salt Pepper Granulated garlic Worchestershire sauce Hamburger bun American or Swiss cheese slice Fresh spinach Purple onion slice, or to taste 1. Place fresh portobello mushroom gill side up on a pancake griddle. Season to taste with salt, pepper, granulated garlic and Worchestershire sauce. Cook for approximately 10 minutes gill side up, then flip and cook for 5 minutes or to desired degree of firmness. 2. Place bun halves on grill cut side down, flip over and place 1 slice of cheese on one bun half. Add mushroom and top with fresh spinach and purple onion. Place the top of the bun on the other portion of the bun and enjoy.