Ingredients
 1/4  cup  low-sodium soy sauce
 1/4  cup  balsamic vinegar
 2  tablespoons  olive oil
 3  garlic cloves, minced
 4  (4-inch) portobello mushroom caps
 1  small red bell pepper
 Cooking spray
 1/4  cup  low-fat mayonnaise
 1/2  teaspoon  olive oil
 1/8  teaspoon  ground red pepper
 4  (2-ounce) onion sandwich buns
 4  (1/4-inch-thick) slices tomato
 4  curly leaf lettuce leaves

Preparation

1. Combine first 4 ingredients in a large zip-top plastic bag; add mushrooms to bag. Seal and marinate at room temperature for 2 hours, turning bag occasionally. Remove mushrooms from bag; discard marinade.

2. Prepare grill to medium heat. (see Tip)

3. Cut bell pepper in half lengthwise; clean and discard seeds. Place pepper halves on grill rack coated with cooking spray; grill 15 minutes until blackened, turning occasionally. Place in a zip-top plastic bag; seal. Let stand 10 minutes. Peel. Reserve 1 pepper half for another use. Finely chop 1 pepper half; place in a small bowl. Add mayonnaise, 1/2 teaspoon oil, and ground red pepper; mix well.

4. Place mushrooms, gill sides down, on grill rack coated with cooking spray; grill 4 minutes on each side. Place buns, cut sides down, on grill rack coated with cooking spray; grill 30 seconds on each side or until toasted. Spread 2 tablespoons mayonnaise mixture on top half of each bun. Place 1 mushroom on bottom half of each bun. Top each mushroom with 1 tomato slice and 1 lettuce leaf; cover with top halves of buns.

Tips & Tricks
Tip: This recipe can also be prepared in the oven under the broiler.  For medium heat place broiler pan 6 - 8 inches below broiler element.

Nutritional Notes: Calories: 251; Fat: 8.4g (sat 2.3g,mono 3.7g,poly 2.1g);  Protein: 7.3g; Carbohydrate: 37.9g; Fiber: 2.4g; Cholesterol: 0.0mg; Iron: 2.2mg; Sodium: 739mg; Calcium: 81mg