Stuffed mushroom and spinach shells

30 jumbo pasta shells
1 medium onion finely chopped
3 cups white mushrooms roughly chopped
2.5 cups shredded mozzarella cheese
2 cups baby spinach
2 cups pasta sauce (I make my own and store it)
2 tbsp olive oil


Preheat oven to 375. Bring very large pot of salted water to boil. Add pasta and bring back to a boil. Boil until al dente. Drain and add cold water to pan to allow pasta to cool. In a large skillet over medium heat add olive oil and onions. Cook for about 3 minutes and add in mushrooms. Toss and cook until mushrooms and onions are soft. Turn off heat and add in spinach and combine. Place half of cheese in pan and combine quickly. Place pasta sauce in the bottom of a 9x13 baking dish. Take a shell out of the water and gently open it. Using your hand fill it with about 2 tbsp of the mushroom mixture. Place it open side up in the pan. After you have filled all of the shells place any remaining mushroom mixture around the shells. Top with other half of cheese. Cover and bake for 20 minutes. Remove foil and turn on broiler. Cook for 5-7 minutes or until cheese browns.