Start the marinara first so it can simmer while you make the meatballs. Dice the onions into small pieces and place in a large pot. Add the olive oil to the pan with the onions. Turn the heat to medium high heat and saute until the onions are tender. While the onions are cooking, add the pepper, oregano, garlic, chopped parsley, salt, brown sugar and cayenne pepper. Continue to saute until the seasonings are fragrant. Add the tomato paste, diced tomatoes and chicken broth and let the sauce simmer until it begins to thicken and the meatballs are cooked.
For the meatballs, chop the onions, dice the garlic, chop the kale, and cut the parsley. Add these items into a mixing bowl. Add the remaining meatball ingredients and combine together until everything is incorporated. Place a cookie sheet on the counter and drizzle with a little olive oil. Spread the olive oil over the bottom of the cookie sheet.
With a scoop or spoon, place a golf ball sized meatball on the cookie sheet. Continue to do this until all of the meat mixture has been formed into balls. Preheat the oven to 400 degrees. Bake the meatballs for 18-22 minutes, or until the meatballs are nice and browned on the bottom and cooked most of the way through (they will continue to simmer in the sauce so they can keep cooking).
If you wish to serve the meatballs over noodles, cook the spaghetti until al dente and then drain and get ready to serve. Remove the meatballs from the oven. If you wish to serve the meatballs together with the sauce, pour a generous portion of the marinara sauce into the bottom of a pan. Place the meatballs into the sauce. Sprinkle with the shredded mozzarella cheese. Put the pan in the oven to broil (if your pan can be baked) until the cheese is melted. Serve the meatballs and sauce over noodles. Garnish with fresh parsley.