Lightly grease the inside of your slow cooker with cooking spray or a little olive oil.
In the slow cooker, add rice, chicken broth, lemon juice, lemon zest, garlic, and onion. Stir to combine.
Season chicken with salt, pepper, oregano, thyme, and paprika. Heat olive oil in a skillet over medium-high heat and sear chicken for 2–3 minutes per side until lightly browned (optional, but adds flavor).
Place chicken on top of rice mixture in the slow cooker.
Cover and cook on LOW for 4–5 hours or on HIGH for 2–3 hours, until rice is tender and chicken is fully cooked (internal temp 165°F / 74°C).
Fluff rice with a fork and adjust seasoning if needed.
Garnish with fresh parsley and lemon slices before serving.