Marinate the Chicken: Combine chicken, olive oil, lemon juice, garlic, and all seasonings. Cover and refrigerate for 1–2 hours.
Make the Sauce: Whisk all white sauce ingredients together. Cover and refrigerate until ready to serve.
Cook the Rice: Melt butter in a saucepan over medium heat. Add washed rice, turmeric, and cumin. Stir for 1 minute. Add chicken broth and bring to a boil. Cover, reduce heat to low, and simmer for 15 minutes. Remove from heat and let rest, covered, for 5 minutes. Fluff with a fork.
Cook the Chicken: Heat a skillet over medium-high heat. Add marinated chicken and sear for 5–6 minutes, turning occasionally, until browned and cooked through to 165°F.
Assemble: Divide rice between bowls and top with chicken and white sauce. Serve with lettuce, tomato, and warm pita if desired.