In a 5- to 6-quart slow cooker, combine the apricot jam, ketchup, soy sauce, ginger, and crushed red pepper. Add the chicken, onion, and garlic and toss to coat. Scatter the red pepper over the top and cook, covered, until the chicken is cooked through, 5 1/2 to 6 1/2 hours on low, or 3 1/2 to 4 1/2 hours on high. Twenty minutes before serving, cook the rice according to package directions. Serve the chicken and sauce on top of the rice and sprinkle with scallions and sesame seeds, if desired.