Heat 1 tablespoon of oil in a large skillet over medium heat. Add the finely chopped onion, sautéing until soft and translucent, about 4-5 minutes. Stir in minced garlic and cook for another minute until fragrant.

Add the cooked shredded chicken to the skillet, along with salt, black pepper, and half of the green chile enchilada sauce. Stir until the chicken is evenly coated.

Remove the skillet from the heat and gently fold in 1 cup of sour cream until fully incorporated. Set the mixture aside to cool slightly.

Warm the small flour tortillas in a microwave for about 30 seconds until pliable. Spoon a generous portion of the chicken mixture across the center of each tortilla.

Carefully roll each tortilla tightly around the filling and place them seam-side down in a greased baking dish.

Pour the remaining green chile enchilada sauce evenly over the top. Sprinkle the remaining Monterey Jack and cheddar cheese over the ensemble.

Preheat your oven to 350°F (180°C) and bake the enchiladas for 20-25 minutes until the cheese is melted and bubbly.

Allow the enchiladas to cool for 5 minutes before garnishing with freshly chopped cilantro if desired.