Sauté Aromatics: In a skillet over medium heat, heat olive oil and sauté the minced garlic and diced onion until fragrant, about 2 minutes. Transfer the sautéed aromatics to the slow cooker.
Layer Ingredients: In the slow cooker, add the uncooked rice, chicken broth, lemon juice, lemon zest, salt, pepper, oregano, paprika, and red pepper flakes. Stir to combine.
Add Chicken: Place the chicken on top of the rice mixture. Cover and cook on low for 5-6 hours or high for 3-4 hours, until the chicken is fully cooked and the rice is tender.
Finish and Serve: Stir in the frozen peas (if using) and let sit for 5 minutes. Shred or slice the chicken as desired. Garnish with fresh parsley and serve hot.