Preheat your oven to 375°F (190°C).
In a small mixing bowl, whisk together the tomato puree, water, ancho chili powder, ground cumin, garlic powder, and onion powder until the sauce is smooth.
Heat the olive oil in a small skillet over medium heat and sauté the diced red onion for 3-4 minutes until translucent and soft.
Place the cooked, shredded chicken in a bowl and toss with the sautéed red onion and 2 tablespoons of the prepared ancho sauce.
Warm the corn tortillas in a dry skillet for 30 seconds per side or wrap them in a damp paper towel and microwave for 20 seconds until they are pliable.
Lay the tortillas flat and divide the chicken mixture evenly between them, rolling them up tightly.
Place the rolled tortillas seam-side down in a small oven-safe baking dish.
Pour the remaining ancho chili sauce over the top of the tortillas and sprinkle evenly with the shredded Monterey Jack cheese.
Bake in the preheated oven for 15 minutes, or until the cheese is melted and bubbly.
Remove from the oven and garnish with fresh chopped cilantro and a pinch of sea salt and black pepper before serving.