1. In a medium bowl, combine pork, onion, zucchini, egg, breadcrumbs, oregano, cumin, 1 1/2 teaspoons salt, and 1/4 teaspoon pepper; mix well with a fork. Form into 16 (2-inch) balls; transfer to a plate, and place in freezer until firm, 10 to 15 minutes.
2. Meanwhile, combine tomatoes and chiles in a blender; process until smooth, and set aside.
3. Heat 1 tablespoon oil in a large, straight-sided skillet over medium-high heat. Add half the meatballs; cook until brown, turning often, 4 to 5 minutes; transfer to a plate. Repeat with remaining oil and meatballs.
4. Reduce heat to medium-low. Add pureed sauce and return all meatballs to skillet. Cover; simmer, stirring occasionally, 30 minutes. Uncover, and simmer until sauce is thickened, 5 to 10 minutes more. Season with salt and pepper. Serve over rice, sprinkled with cilantro, as desired.