01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - Brush both sides of the portobello caps with olive oil and season with salt and pepper. Place gill-side up on the baking sheet.
03 - In a medium bowl, combine ricotta, mozzarella, Parmesan, egg, basil, garlic, oregano, salt, and pepper. Mix until smooth.
04 - Spoon a thin layer of marinara sauce into each mushroom cap (about 1 tablespoon per cap).
05 - Fill each mushroom with the ricotta mixture, dividing evenly among all caps.
06 - Spoon remaining marinara sauce over the ricotta filling in each cap.
07 - Top each stuffed mushroom with shredded mozzarella and Parmesan.
08 - Bake for 25-30 minutes, until mushrooms are tender and cheese is golden and bubbly.
09 - Let cool slightly. Garnish with fresh parsley or basil, if desired.
10 - Allow cooked mushrooms to cool completely. Wrap each tightly in foil and place in a freezer-safe container. Freeze for up to 2 months. To reheat, thaw overnight in the refrigerator and bake at 375°F for 15-20 minutes, or until heated through.