Preheat the oven to 375°F (190°C).
Heat olive oil in a large oven-safe skillet over medium-high heat.
Season the chicken thighs with salt and pepper.
Place the chicken skin-side down and cook for 5–6 minutes until golden brown. Flip and brown the second side for another 5–6 minutes. Remove and set aside.
In the same skillet, cook the onion, garlic, and mushrooms until softened.
Add the spinach and cook until wilted, working in batches if necessary.
Stir in the brown rice, chicken broth, thyme, oregano, smoked paprika, remaining salt, and pepper.
Return the chicken thighs to the skillet, skin-side up.
Bake for 30–35 minutes, or until the rice is tender and the chicken reaches an internal temperature of 165°F (74°C).
Allow the Skillet Chicken and Rice with Spinach and Mushrooms to rest for 5 minutes before serving.