1. Heat oven to 375°F.
2. Remove stems from mushrooms; chop stems. Use spoon or sharp knife to scrape gills from caps; discard gills. Brush 1 Tbsp. dressing onto rounded sides of caps.
3. Line the bottom of the baking pan with foil paper. Then place rounded-sides down.
4. Heat remaining dressing in large saucepan on medium-high heat. Add chopped stems, peppers and garlic; cook and stir 2 min.
5. Add spinach, then cover. Simmer on medium-low heat 4 min or until spinach is wilted, stirring after 2 min. Spoon over mushroom caps; top with cheese.
6. Bake 18 to 20 min. or until mushrooms are tender. Enjoy!