To a large mixing bowl add ground beef, rice, onion, green bell pepper, garlic, 3 tbsp parsley, the Italian seasoning, egg, salt and pepper. Mix together fairly well with your hands until even combined.
Scoop out mixture about 2 slightly heaping tablespoons at a time (43g) each and compress and roll into balls (about 1 1/2-inches each). Set on a baking sheet or plates as you shape them.
Heat olive oil in a large pot over medium-high heat. Add half the meatballs spacing evenly apart. Let sear on bottom until golden brown, about 1 - 2 minutes. Carefully turn to opposite side (meatballs can be fairly delicate) and let brown on opposite side about 1 - 2 minutes longer.
Transfer browned meatballs back to baking sheet, then add remaining half of the meatballs and brown on each side.
Return meatballs on baking sheet to pot then right away pour in tomato sauce, chicken broth, Worcestershire, and red bell pepper. Bring mixture just to a simmer.
Cover and reduce heat to low. Let simmer until meatballs are cooked through and tender, about 25 to 30 minutes, gently tossing meatballs once halfway through.
If desired thin with more chicken broth. Serve warm garnished with remaining 1 Tbsp parsley and optional shredded mozzarella (not included in nutrition estimate).
To Make Oven Baked Porcupine Meatballs:
Skip the browning.
Pour the sauce over the formed meatballs in a large baking dish (such as a lasagna pan).
Cover with foil and bake 350 degrees until meatballs are cooked through and tender, about 1 hour.