This epic Portobello Mushroom Burger is easy, balsamic marinated and stacked high with arugula, sliced tomato, red onion, dairy-free cheese, and pickle, then placed in a toasted brioche bun and smothered in Smoky Homemade Chipotle Sauce. Made with grilled Portobello mushrooms, cook on the grill, stove top, or in the oven.