Place onion, red pepper and garlic in a 6-quart slow cooker. Add chicken, broth, 3/4 teaspoon salt, oregano and pepper.
Cover and cook on low for 5 to 6 hours until chicken reaches 165°F and is tender around the bones. Lift chicken onto a clean plate and strain the liquid into a heatproof measuring jug, reserving the cooked vegetables.
Skim fat from the liquid. Measure exactly 2 3/4 cups, adding only as much of the listed water as needed to reach that amount; reserve any excess broth for another use.
Heat oil in a saucepan over medium heat and stir rice and turmeric for 1 minute. Add the measured liquid and remaining salt, bring to a boil, cover and cook on low for 18 minutes.
Add peas over the rice, cover again off the heat and rest for 10 minutes. Meanwhile, remove and discard all bones and cartilage from the chicken and pull the meat into large pieces.
Fluff rice and gently fold in chicken and reserved vegetables. Heat over low heat, covered, for 3 to 5 minutes until everything is hot throughout, then divide among 6 servings.