Preheat the oven to 375°F (190°C).
Heat olive oil in a large skillet over medium heat. Add the chopped onion and cook for 3-4 minutes until softened.
Add the minced garlic, ground cumin, chili powder, salt, and black pepper to the skillet. Cook for 1 minute until fragrant.
Add the chopped spinach to the skillet and cook until wilted, about 2-3 minutes. Remove from heat.
In a large bowl, combine the shredded chicken, cooked spinach mixture, and 1 cup of shredded cheddar cheese and 1 cup of shredded Monterey Jack cheese. Mix well.
Spread 1/2 cup of enchilada sauce evenly on the bottom of a 9×13 inch baking dish.
Warm the tortillas slightly to make them pliable. Spoon about 1/3 cup of the chicken and spinach filling down the center of each tortilla.
Roll up each tortilla tightly and place seam side down in the baking dish.
Pour the remaining enchilada sauce evenly over the rolled tortillas.
Sprinkle the remaining 1 cup cheddar cheese and 1 cup Monterey Jack cheese evenly on top.
Cover the baking dish with aluminum foil and bake for 15 minutes.
Remove the foil and bake for an additional 10 minutes, or until the cheese is melted and bubbly.
Let the enchiladas rest for 5 minutes before serving.