Preheat oven to 425 degrees.

Spray a small baking sheet with non-fat cooking spray, and place peppers on it, cut side down. Roast until peppers begin to become tender, about 10 minutes. Remove from oven and set aside.

Spray a large nonstick skillet with non-fat cooking spray and set over medium-high heat.

Add onion and garlic, and cook, stirring often, until soft and beginning to brown, 2 to 3 minutes.

Add mushrooms and pepper and cook, stirring often, until the vegetables are wilted and soft, about 7 minutes.

Reduce heat to low; sprinkle the mushrooms with flour and stir to coat. Stir in broth and soy sauce; bring to a simmer.

Divide the mixture into 2 portions then scoop one portion onto each pepper half. Top each with one slice of the cheese, and place back in oven or under a broiler until the cheese melts. Serve immediately.