Heat a 12-inch cast-iron skillet over medium heat and add the remaining oil. Cook your chicken thighs with the skin side down for 15 minutes, until the fat has rendered out. Turn the heat off, add the tomatoes, and swirl around the rendered fat. Flip the chicken thighs so they are skin side up. Add the lemon slices and thyme sprigs over the chicken, and transfer the skillet to the oven. Roast for 18 minutes.