Preheat the oven to 375°F (190°C).
Heat olive oil in a large skillet over medium heat. Add chopped onion and cook for 3-4 minutes until softened.
Add minced garlic, ground cumin, chili powder, salt, and black pepper to the skillet. Cook for 1 minute until fragrant.
Add chopped spinach to the skillet and cook until wilted, about 2-3 minutes. Remove from heat.
In a large bowl, combine shredded chicken, cooked spinach mixture, and 1/2 cup of cheddar cheese and 1/2 cup of 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 corn tortillas in a microwave or on a skillet until pliable.
Spoon about 1/4 cup of the chicken and spinach mixture onto each tortilla, roll it up tightly, and place seam side down in the baking dish.
Pour the remaining enchilada sauce evenly over the rolled tortillas.
Sprinkle the remaining cheddar and Monterey Jack cheese evenly on top.
Cover the baking dish with aluminum foil and bake for 20 minutes.
Remove the foil and bake for an additional 10 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let cool for 5 minutes before serving.