Preheat oven to 350 degrees.
Prepare jumbo shells per instructions on back of package. Drain and rinse. (Cooking the pasta to al dente will allow for ease of stuffing the pasta. They will finish cooking in oven.)
In a large skillet over medium high, heat 1 TBS cooking oil and 1 TBS butter. Cook peppers and onions until softened. Season with salt & pepper. Add in ground beef and further cook until beef is no longer pink. Stir in minced garlic for 1 minute. Turn off heat.
In a medium bowl, mix together 2 cups mozzarella cheese, cottage or ricotta cheese, parmesan cheese, 2 tsp Italian seasoning, 1/8 tsp black pepper, and 1 egg. Pour cheese mixture into the beef mixture and mix well.
Butter or spray a 9 x 13 baking dish. Spread 1/4 cup of pasta sauce onto bottom of dish.
Stuff each shell with 2 TBS of mixture and place into baking dish. Continue until shells are filled. In the jar of remainder of sauce fill with 1/4 cup of water and shake well. Pour sauce all over the stuffed pasta shells. Sprinkle 1 - 2 cups of mozzarella cheese covering the sauce. Sprinkle with extra Italian seasoning.
Cover & seal baking dish with foil. (To keep cheese from sticking to foil, I lightly spray the foil with cooking spray and place the sprayed side down on the cheese.)
Place in preheated oven for 40 minutes. Remove foil and cook an additional 10 minutes until cheese is golden brown. Let sit for 5 -7 minutes before serving. Garnish with parsley if desired.