Preheat oven to 350° F and prepare brown rice either on stove top or in Instant Pot.
Use a serrated knife and cut pepper segments to form rings, about 1.5 inch in thickness, and remove pith from inside of rings. Discard ends and then set the rings aside.
Remove sausage from links (or use bulk) and place in medium-size mixing bowl. Add 1/4 marinara sauce and reserve the rest.
Combine the rest of the ingredients and mix thoroughly.
Place 1/2 cup to 3/4 cup marinara sauce in an 11 x 13" baking pan and spread evenly. Evenly set the cut pepper rings on top of the sauce. Next, using a small handful of the meat mixture, form a small ball and place in each pepper ring, ensuing a uniform amount for each portion.
Use about a cup of reserved marinara sauce and top each portion evenly. Cover baking pan with foil and bake for 45 minutes. Then, remove foil and bake another 15 minutes.
Remove the stuffed pepper rings from oven and raise the oven rack to the highest position possible. Turn the oven broiler to low and sprinkle Parmesan cheese on each mound of meat. Place in oven, under broiler, for 2 or 3 minutes until the cheese just starts to brown. Remove from oven and garnish with chopped fresh parsley. Serve with additional (warmed) marinara sauce if desired.