Begin the recipe by cooking the 20 jumbo shells pasta according to the package directions. Try not to overcook the pasta and once it has finished, carefully drain the shells pasta from the water and set it aside. Preheat the oven to 350 degrees F.
In a large skillet over medium-high heat add the ⅓ cup diced onion and ¼ teaspoon salt. Cook and stir constantly for 1 minute. Add in the ½ pound ground Italian sausage (mild or hot), 2 cloves minced garlic, ½ teaspoon Italian seasoning, and ½ cup green bell pepper.
Cook until the onion is translucent and the sausage is cooked thoroughly. Stir in 2 ounces of the quartered or mini pepperoni. Remove the skillet from the heat and stir in ½ cup shredded mozzarella cheese.
Grab the 20 cooked jumbo shells and fill each one with the sausage mixture and place in an 8x8-inch square baking dish with the open seam side down. Using plastic glove covered hands makes this process much easier.
Evenly top the shells with the pasta sauce and the rest of the 2 ounces of pepperoni.
Spread the 1 cup of mozzarella cheese evenly over the top, cover with aluminum foil, and bake covered for 20 to 25 minutes.
Carefully remove the aluminum foil and continue baking for an additional 5 to 10 minutes, until the cheese is hot and bubbly. Remove the stuffed shells from the oven and serve warm. Enjoy!
Store any leftovers in the refrigerator in an airtight container for 3 to 4 days. Just reheat in the microwave or in the oven. If you heat your pasta in the oven, cover the pan to prevent the shells from drying out.