In a large shallow dish, whisk together the white wine vinegar, 3 tablespoons olive oil, ¼ teaspoon salt and ¼ teaspoon pepper.

Add the mushrooms, turn to coat and let rest for 20 minutes.

Preheat the grill to medium-high heat. Brush the grill with canola oil.

In a medium bowl, combine black beans and olive oil. Mash with a fork until the black beans are crushed and the mixture starts to stick together.

Stir the cumin, ¼ teaspoon salt and ¼ teaspoon pepper into the black beans.

Heat the remaining ½ teaspoon olive oil in a medium skillet. Add the garlic and saute for 30 seconds.

Add the red bell pepper and jalapeño pepper, and cook, stirring occasionally, until the peppers are tender, about 3 minutes. Stir in the corn kernels.

Reduce the heat to medium-low and add the black bean mixture, stirring until the mixture is heated and combined.

Place the mushrooms on the grill, gill side down, and cook until the mushrooms are tender, 3 to 5 minutes per side (depending on the thickness of the mushrooms).

In the last 2 minutes of cooking, divide the black bean mixture and the queso fresco evenly between the 4 mushrooms.

Garnish the mushrooms with minced cilantro and serve immediately. Top with salsa and diced avocado, if desired.