Pre-heat the oven to 425. Lightly mist a 9×13 baking dish with cooking spray and set aside.

In a medium bowl, mix together the barbecue sauce, tomato sauce, garlic, chili powder and cumin until thoroughly combined and set aside.

In a large skillet or sauté pan, bring the oil to medium heat. Add the chopped onions and cook for a couple minutes until they start to soften and become fragrant. Add the chicken breasts in a single layer and cook for 3 minutes on one side, flip them over, and then continue to cook for 2-3 minutes on the other side. Add the sauce mixture to the pan and bring it to a boil. Lower the heat to low and cover the pan. Simmer for 15-20 minutes, occasionally removing the lid to stir the sauce, until the chicken is fully cooked through.

Remove the pan from heat and transfer each breast to a cutting board, shredding it using two forks. Transfer the shredded chicken to a large mixing bowl. Add ½ cup of the sauce from the pan to the chicken along with 2 ounces (about ½ cup) or the shredded cheese. Mix everything in the bowl together until well combined.

Microwave the tortillas for 30-60 seconds on high until warm and soft. Spread 1/4 cup of the chicken mixture onto a tortilla and tightly roll it up. Place the rolled tortilla seam side down in the prepared baking dish and repeat with the remaining tortillas. Spray the tops of the rolled tortillas with cooking spray and bake in the oven for 8 minutes until tortillas are slightly crispy.

Reduce the heat to 400 and pour the remainder of the sauce evenly over the tops of the enchiladas, followed by the remaining 2 ounces of shredded cheese. Place back in the oven for an additional 18-20 minutes. Sprinkle the sliced scallions over the top of the entire dish and serve.