Heat oil in a large skillet over medium-high heat.
Season chicken thighs with salt, pepper, and garlic powder and place skin side down in the hot skillet. Cook undisturbed until well browned, crisp, and releases easily from the skillet, 6 to 7 minutes.
Flip chicken and cook an additional 1 to 2 minutes. Remove chicken from the pan and set aside (chicken will not be cooked through at this point).
Add onion to the drippings in the pan, and cook until slightly softened, about 2 minutes. Add tomatoes, and cook until tomatoes soften and begin to burst, 4 to 5 minutes. Stir in beans and remaining salt and pepper.
Return chicken to the pan, skin side up, along with any juices that have accumulated. Return to a simmer; cover, reduce heat slightly, and cook until chicken is tender and cooked through, 25 to 30 minutes. An instant read thermometer inserted near the center should read 165 degrees F (74 degrees C).
Transfer chicken to a serving platter. Stir in spinach until wilted and then add in Boursin. Stir until melted and heated through. Season to taste with more salt and pepper.
Serve chicken over bean stew.