For a hearty and satisfying veggie dinner, try a grilled portobello mushroom burger. Marinate the portobello mushrooms in a mixture of balsamic vinegar, soy sauce, and garlic for extra flavor. Grill the mushrooms until they are tender and juicy. Assemble the burger with a toasted bun, a spread of your favorite sauce (such as barbecue or aioli), lettuce, tomato, and any other toppings you desire. The meaty texture of the portobello mushrooms makes this burger a great alternative to traditional meat burgers.