Combine the onion, jalapeno and oil in a large saucepan over medium heat. Cook, stirring often, until the onions and peppers have softened, about 10 minutes.

Stir in the garlic, chili powder, cumin, salt and sugar, and cook just until fragrant, less than 30 seconds.

Mix in the tomato sauce and water and bring to a simmer.

Lower the heat and cook until slightly thickened, about 5 minutes.

Nestle the chicken into the sauce. Reduce the heat to low, cover and cook until the chicken is completely cooked through (160˚ F on an instant-read thermometer), about 20 minutes.

Transfer the chicken to a plate and set aside to cool.

Strain the sauce through a large mesh strainer into a medium bowl. Transfer the reserved solids to a large bowl and set aside. Season the sauce with additional salt and pepper to taste.

Shred the chicken into bite size pieces and add to the bowl with the onion mixture. Add in ¼ cup of the sauce, 1 cup of shredded cheese, and the cilantro. Stir to combine.

Preheat the oven to 275˚ F. Oil a 9 x 13" baking dish with cooking spray.

Wrap your stack of tortillas in a damp towel/paper towel and microwave for 30-45 seconds, until warm and pliable.

Spoon 1/3 cup of the chicken mixture evenly down the center of a tortilla. Roll up the tortilla around the filling tightly, and place in the prepared baking dish, seam-side down.

Repeat with the remaining filling and tortillas.

Bake for 25 to 30 minutes or until warmed through and cheese is bubbly and top starting to brown.

Garnish with additional cilantro and sliced avocado and serve!