Italian Meatball Stuffed Mushrooms

(1) 24 oz. package white button mushrooms, cleaned and stems removed

bag Italian style frozen meatballs

packed cups baby spinach, roughly chopped

olive oil

diced onion

diced red bell pepper

cream cheese, at room temperature

shredded parmesan cheese, plus 2 tablespoons for garnish

salt

ground black pepper

garlic powder