Preheat oven to 350°F.

Heat the oil in a large nonstick skillet over medium heat. Season the chicken thighs with ½ teaspoon kosher salt. Place the chicken in the pan and cook until golden brown on the bottom, about 4–5 minutes. Flip and continue cooking until golden brown on the other side, about 4–5 more minutes.  

Remove the chicken and place on a cutting board. Add the onion and cook, stirring occasionally, until translucent, about 3–4 minutes. Remove the skillet from the heat.

Empty the enchilada sauce into a 2-cup measuring cup. You’ll have a scant 2 cups.

Chop the chicken into ½ inch pieces. Add it back to the skillet with the red onion. Add the black beans, 1 cup queso fresco, and ⅓ cup of the enchilada sauce. Stir to combine.

Pour ½ cup enchilada sauce into the bottom of a 13x9 inch pan. Tip the pan until the sauce covers the entire bottom.

Place a tortilla on a flat surface. Using a pastry brush, brush the tortilla lightly with some of the remaining enchilada sauce. Place a heaping ½ cup of the meat and bean mixture down the center of the tortilla. Roll the tortilla, making sure that the filling doesn’t escape. Place the filled tortilla in the pan. Repeat with the remaining 7 tortillas.

Pour the remaining enchilada sauce over the tortillas. Top with 1.5 cups of Mexican blend cheese.

Bake for 20 minutes, or until the cheese is melted and the filling is bubbly. Top with cilantro and additional queso fresco if desired, and serve.