In a skillet, heat olive oil over medium heat. Add the chopped onion and cook until softened. Stir in the shredded chicken, cumin, chili powder, salt, and pepper. Cook for an additional 2-3 minutes to combine the flavors.
Preheat oven to 375°F (190°C). Lay each flour tortilla flat and spoon some of the chicken mixture into the center. Add a generous amount of shredded cheddar and Monterey Jack cheese. Roll the tortillas up and place them seam-side down in a greased baking dish.
In a saucepan, combine the sour cream, heavy cream, chicken broth, garlic powder, smoked paprika, cayenne pepper (if using), and a pinch of salt. Heat over medium heat, stirring constantly until the sauce thickens, about 5-7 minutes.
Pour the creamy sauce evenly over the enchiladas. Top with any remaining shredded cheese. Bake for 20-25 minutes, or until the cheese is melted and bubbly.
Once baked, top each enchilada with a spoonful of salsa and garnish with fresh cilantro if desired. Serve hot and enjoy the creamy, cheesy goodness!