Here’s the vegetarian answer to Sloppy Joes—edamame lightens up a black bean mixture to keep these sliders from tasting too dense.
Big or small, portobello mushrooms make the perfect grilled "burger." Portobellos' meaty texture and rich, robust flavor take on the flavors of marinades and rubs and stay juicy and tender when grilled. The onion topping can be made up to two days ahead.