Preheat the oven to 400°F (200°C). Pat the chicken thighs dry with paper towels.
In a small bowl, combine garlic powder, smoked paprika, ground cumin, ground coriander, and salt; reserve half of the spice mix.
Generously season both sides of the chicken with about half of the spice blend and sprinkle with the black pepper.
Heat the olive oil in a large heavy-duty cast iron skillet over medium-high heat. Sear the chicken thighs skin-side down until golden, about 4 minutes, then flip and sear the other side about 4 minutes. Transfer the chicken to a plate.
Add the diced onion and diced bell pepper to the same pan and sauté for about 2 minutes until softened.
Add the minced garlic and cook 30 seconds until fragrant, then stir in the diced tomatoes, diced jalapeño, tomato paste, and the remaining spice blend; cook 2–3 minutes until tomatoes begin to soften.
Stir in the rice, frozen peas, and chopped cilantro, then briefly sauté to coat the rice with the tomato mixture.
Add the water and bring the pan to a simmer, then nestle the seared chicken thighs on top of the rice mixture.
Cover the skillet tightly with foil and transfer to the preheated oven. Bake until the chicken is cooked through, the rice is tender, and liquid is absorbed, about 30 minutes.
Optionally, for crispier skin, place the skillet under the broiler for 4–5 minutes after baking. Remove the chicken, fluff the rice with a fork, garnish with additional chopped cilantro, and serve.