Heart-Healthy Balsamic Portobello Sandwich Recipe

Ingredients

• 2 portobello mushrooms caps, washed
• 1/2 red onion, peeled and cut into 1/4-inch thick slices
• 1 Tbsp balsamic vinegar
• 1 tsp olive oil
• Black pepper to taste
• 2 oz sliced reduced-fat provolone cheese
• 2 light multigrain rolls, split
• 1 roasted red bell pepper, sliced
• 1/2 cup fresh baby spinach
• 1/2 tomato, sliced