Heat oven to 375 degrees.
Season the chicken thighs with complete seasoning, Italian seasoning, curry powder or turmeric, smoked paprika, adobo, salt, and pepper. Heat the olive oil in a cast iron skillet or any oven-safe pan on medium high heat and sear the chicken skin side down until golden, about 6 to 7 minutes per side. Remove the chicken and set it aside.
Add the diced onion, red pepper, and garlic to the same pan and sauté until fragrant, about 2 minutes. Push the aromatics to the side of the pan and add the lemon slices to the center. Sear them until browned and fragrant, about 2 minutes per side, then remove and set aside.
Pour the rice into the pan and stir to coat it in all the remaining flavor. Add 2 cups of water or chicken broth, season with salt and pepper, and bring the mixture to a simmer. Stir in the chopped frozen spinach so it melts into the rice.
Nestle the chicken thighs back into the pan, skin side up, and place a seared lemon slice on top of each piece. Cover the pan with foil or a lid and bake at 375°F for 30 minutes. Remove the cover and continue baking for 10 to 15 minutes, or until the chicken is cooked through and the liquid has mostly absorbed.
Let the dish rest for a few minutes before serving. Spoon the tender lemony spinach rice around each chicken thigh and enjoy.