In a skillet over medium heat, brown and crumble the sausage, breaking it into pieces as it cooks. Drain any excess fat and remove from heat.
In the same saucepan, cook spinach until wilted or about 1-2 minutes.
Cook the shells according to package directions (try not to over cook the shells because they will get cooked more in the oven).
In a mixing bowl, combine the ricotta, 4oz of mozzarella, 1/4 cup of Parmesan, egg, oregano, and garlic powder. Stir in the spinach and about 3/4 of the cooked sausage. *this is where you would add in any additional diced veggies*
Coat the bottom of a 9x13in pan with all of the spaghetti sauce. Spoon the cheese & sausage mixture into the shells and place shells open side up, very close together in the dish.
Sprinkle the remaining sausage over the top of the shells. Then sprinkle with the rest of the mozzarella and Parmesan cheese.
Cover with aluminum foil and bake at 350 °F for 25-35 minutes or until the cheese is bubbly. Then remove foil and broil it on high for 3-5 minutes until cheese starts to get golden brown (watch closely because it can burn quickly).
Allow to cool for a few minutes. Top with parsley and serve warm.
