Pat the chicken thighs dry and season generously with salt and pepper. Heat olive oil in a wide, heavy skillet over medium-high heat. Brown the thighs until deeply golden, 4–5 minutes per side. Remove and set aside.
In the same pan, add the sliced sausage. Let it take on color, then remove. Don’t wipe the pan—you want those browned bits.
Add the onion and cook until soft and lightly caramelized. Add garlic and tomato paste. Cook the paste until it turns dark brick-red and smells sweet, 2–3 minutes.
Stir in paprika, cumin, and red pepper flakes. Add the rice and stir until glossy and coated, about 30–60 seconds.
Add hot stock, scraping up the bottom of the pan. Nestle the chicken thighs back in, scatter the sausage around them, cover, and bring to a simmer. Reduce heat to low and cook 18–20 minutes, until the rice is tender.
Stir in the drained beans during the last 5 minutes, just to warm through and bind the dish.
Turn off heat and let the pan rest, covered, for 5 minutes. Fluff the rice, finish with black pepper, herbs, or lemon if you like, and serve straight from the skillet.