Mix the small chopped onion, minced meat, and egg together in a bowl. Season with salt, pepper, and Worcestershire sauce. Shape the mixture into balls.
Heat the oil in a large pan over medium-high heat. Fry the meatballs for 8-10 minutes, turning occasionally, until browned on all sides. Remove and set aside.
In the same pan with the remaining oil, braise the peeled tomatoes and the finely chopped vegetable onion over medium heat for 5 minutes.
Stir in the kidney beans, green peppers, and red bell pepper. Cook for 9 minutes over medium heat.
Season with salt, chili powder, mustard, and tomato ketchup. Add the meatballs back and stir to combine.