Preheat your oven to 375 F.

Spray a square glass baking dish with cooking spray and set aside.

Peel the onions and trim off the top inch with a sharp paring knife. Trim off the bottom 1/4 inch of the onions so that they stand upright when placed in your baking dish. Using a spoon (a grapefruit spoon works great for this task), scoop out the center part of the onion flesh, leaving about a 1/2 inch of edge for each onion. Place onions, cavity side up, in your baking dish and set aside.

Chop the onion flesh that you have scooped out of the onions. Heat oil in a large skillet to medium-high. Add sausage, making sure to break up the sausage into bite-sized pieces with a spatula. Add chopped onions to pan. Cook until sausage is browned through, about 8-10 minutes. Add garlic and Italian seasoning and cook for one more minute. Remove from heat and let stand until the sausage mixture is cool enough to handle.

Once sausage mixture has cooled, fold in cheese and rice. With your (clean) hands, gently pack some of the sausage mixture into each onion cavity; repeat this process until the onions have all been stuffed. Spoon a heaping tablespoon of marinara sauce over the top of each onion, letting the sauce drain down into the sausage mixture.

Pour abut 1/4 inch water into the bottom of the baking dish and cover with foil. Bake for 20-25 minutes until the onions are fork-tender and the filling is heated through. Remove from oven, let stand for a few minutes, garnish with parsley and serve.