Preheat oven to 400° F. Line Sheet Pan with Sheet Pan Liner.
Remove mushroom stems and use a spoon to scrape out and discard gills. Place mushroom caps in an Epicure Steamer or a microwaveable bowl. Drizzle with oil and sprinkle with seasoning; gently toss to coat. Cover and microwave on high 4 min.
Meanwhile, dice pepper.
When mushrooms are cooked, place on sheet pan with underside of caps facing up. Divide sauce, cheese, and pepper between caps. Bake 8–10 min, or until cheese is bubbly.
