Preheat the oven to 400°F (200°C) and lightly spray a 13 x 9-inch baking dish with olive oil spray.
Make the sauce: heat 1 teaspoon olive oil in a medium pot over medium heat and add 2 minced garlic cloves; sauté 30 seconds.
Add 1–2 tablespoons chopped chipotle chiles in adobo, 1/2 teaspoon chipotle chili powder, 1/2 teaspoon ground cumin, 3/4 cup chicken broth, 1 1/2 cups tomato sauce, and salt and pepper to taste; bring to a boil then reduce heat and simmer 5–10 minutes. Set aside.
Make the filling: heat a medium skillet over medium-high heat and lightly coat with oil spray or a little olive oil.
Sauté 1 cup diced onion and 2 minced garlic cloves over medium-low heat until softened, about 2 minutes.
Add 10 oz cooked shredded chicken, 1/4 cup chopped cilantro, kosher salt to taste, 1 teaspoon cumin, 1/2 teaspoon dried oregano, 1 teaspoon chipotle chili powder, 1/3 cup chicken broth, and 1/2 cup tomato sauce; cook 4–5 minutes until warmed and combined. Remove from heat.
Assemble enchiladas: place about 1/3 cup of the chicken mixture down the center of each tortilla and roll tightly; place seam-side down in the prepared baking dish.
Spoon the prepared sauce evenly over the rolled enchiladas, then sprinkle 1 cup shredded Mexican cheese blend over the top.
Cover the dish with foil and bake on the middle rack for 20–25 minutes, until heated through and the cheese is melted.
Remove foil, garnish with chopped scallions or cilantro, and serve with optional toppings like sour cream, avocado, or jalapeños.