1. Preheat broiler to high.
2. Place tomatillos on a baking sheet or jelly-roll pan coated with cooking spray. Broil 8 inches from broiler for 15 minutes or until skins blacken and tomatillos are soft.
3. Place tomatillos, pan juices, 3/4 cup onion, and next 4 ingredients (through chopped jalapeño) in a blender or a food processor; process until sauce is almost smooth.
4. Heat a Dutch oven over medium-high heat. Add 1 tablespoon oil to pan; swirl to coat. Sprinkle pork evenly with 1/4 teaspoon salt and black pepper. Add pork to pan. Sauté 6 minutes, turning to brown on all sides. Add tomatillo mixture to pan; bring to a boil. Cover, reduce heat, and simmer 1 hour or until pork is very tender, stirring occasionally.
5. Heat a large saucepan over medium-high heat. Add remaining 1 tablespoon oil to pan; swirl to coat. Add remaining 1/4 cup onion; sauté 2 minutes or until soft. Add rice; sauté 3 minutes, stirring frequently. Add remaining 1/4 teaspoon salt, tomatoes, and 1 cup water to pan; bring to a boil. Cover and simmer 15 minutes or until liquid evaporates and rice is tender; do not stir. Divide rice among 4 plates. Top with pork mixture; garnish with sliced jalapeño and cilantro leaves, if desired.