Cheese and Spinach Stuffed Portebellos

4 large portobello mushroom caps
1/4 tsp. salt
1/4 tsp. freshly ground pepper, divided
1 cup part-skim ricotta cheese
1 cup finely chopped fresh spinach
1/2 cup finely shredded Parmesan cheese, divided
2 T finely chopped kalamata olives
1/2 tsp. Italian seasoning
3/4/ cup prepared marinara sauce

1. Preheat oven to 450 degrees. Coat a rimmed baking sheet with cooking spray.
2. Place mushroom caps, gill-side up, on the prepared pan. Sprinkle with salt and 1/8 tsp. pepper. Roast until tender, 20 t0 25 minutes.
3. Meanwhile, mash ricotta, spinach, 1/4 cup Parmesan, olives, Italian seasoning and the remaining 1/8 tsp. pepper in a medium bowl. Place marinara sauce in a small bowl, cover and microwave on high until hot, 30 seconds to 1 1/2 minutes.
4. When the mushrooms are tender, carefully pour out any liquid accumulated in the caps. Return to caps to the pan gill-side up. Spread 1 T marinara into each cap; cover the remaining sauce to keep warm. Mound a generous 1/3 cup ricotta filling into each cap and sprinkle with the remaining 1/4 cup Parmesan cheese. Bake until hot, about 10 minutes. Serve with the remaining marinara sauce.