Combine the onion, garlic, herbs, and rice in a food processor and pulse until coarsely ground. Transfer to a large bowl and add the meat and egg, along with 2 teaspoons salt and 1 teaspoon pepper. Mix well. The mixture should be dry and easy to form into balls. At this point, you can cover the meat and refrigerate for 24 hours.
Form the meat into balls the size of heaping tablespoons. Heat a large skillet over medium heat with 3 tablespoons of the oil. Add half of the meatballs and brown them for 6-8 minutes. Remove, and brown the rest in the remaining 3 tablespoons of oil.
Caramelize the remaining half an onion in the oil that’s left in the skillet. Add the tomato paste, water, and 1 teaspoon salt. Bring to a boil, then lower the heat and place the meatballs in the sauce. Cover and simmer gently for 30 minutes, or until the meatballs are cooked through. Season with salt and pepper, and garnish with chile flakes. Serve warm, with salad and a fluffy cooked grain like rice or quinoa.