Pat the chicken thighs dry and place them in a large bowl. Add the merquen and 1 ½ tablespoons of the olive oil. Using your hands, rub the oil and spice mixture into the chicken. Arrange the chicken thighs on one of the prepared baking sheets. Season generously with salt and pepper. Place in the oven and roast for 25 minutes, or until a meat thermometer registers 165 degrees F.
Arrange the tomatoes on the second baking sheet. Drizzle with the remaining ½ tablespoon olive oil. Season with salt and pepper. Place in the oven for the last 15 minutes while the chicken is baking.
Remove the chicken and the tomatoes. Let sit for 5 minutes.
Arrange the chicken on a platter with the tomatoes. Scatter the cilantro leaves on top.
*Merquen (or merken) is a Chilean spice blend found at specialty markets made from smoked aji chili, coriander, and salt. (You can also order this online.) Alternatively, you can make your own version using 1 ½ teaspoons smoked Spanish paprika, ½ teaspoon red pepper flakes, ½ teaspoon coriander, and ½ teaspoon salt.