Sprinkle beef with 1/2 teaspoon each of the salt and black pepper. Heat oil in a large heavy skillet over medium-high. Cook beef, in batches, turning to brown on all sides, about 1 minute per side. Whisk together stock, soy sauce, and tomato paste in a small bowl.
Place bell peppers and onion in a 5 1/2- to 6-quart slow cooker, and sprinkle with remaining 1/2 teaspoon salt and 1/4 teaspoon black pepper. Place beef on vegetables, and pour stock mixture over beef and vegetables. Cover and cook on LOW until beef is tender and vegetables are softened and beginning to caramelize, about 7 hours.
Divide hot cooked yellow rice among 4 bowls. Using a slotted spoon, spoon bell peppers and onions over rice. Top with beef, sauce from slow cooker, and cilantro.