Preheat oven to 375°F and lightly grease a 9x13-inch baking dish.
Spread uncooked rice evenly in the bottom of the baking dish, then scatter diced onion and minced garlic over the rice.
Pour chicken broth over the rice mixture and stir gently to combine.
Pat chicken thighs dry and rub with olive oil, then season both sides with paprika, thyme, salt, and pepper. Place chicken thighs skin-side up on top of the rice.
Cover tightly with aluminum foil and bake for 40 minutes, then remove foil and bake for an additional 10 minutes until chicken skin is crispy and rice is tender.
Let stand for 5 minutes before serving. Stir in frozen peas during the last 5 minutes of baking if using.