In this video, learn how to make portobello mushroom burgers, the steak of veggie burgers. This classic vegetarian recipe will make meatless Mondays in your house a highlight. Use large, fresh mushroom caps that have been thoroughly cleaned for the best results. This dish comes together quickly, and it only takes about a half hour to make. Serve these flavor-packed caps on buns with lettuce, tomato, and aioli sauce.