Heat the butter in a 12-inch skillet over medium heat. Add the onion and cook for 2 minutes. Add the mushrooms and cook for 3 minutes longer. Stir in the jalapeno, cumin and chili powder. Add the spinach and cook until the spinach is wilted, stirring frequently.
Mix the sour cream and milk in a small bowl. Stir 2 tablespoons of the sour cream mixture into the spinach. Stir in the chicken and cook until thoroughly heated.
Spray an 8x10-inch baking dish with cooking spray. Heat the oil in a small skillet. Quickly dip each tortilla into the oil to soften. Drain oil from the tortillas.
Spoon the spinach filling across each tortilla and roll up, placing seam side down in the dish. Spoon the remaining sour cream sauce over the enchiladas. Top with the shredded cheese and green chiles.
Bake the enchiladas for 15 minutes or until the cheese is melted and the sauce is bubbly.