Preheat oven to 450 degrees F.
Heat oil in a large cast-iron skillet (12-inch) over medium-high heat. Add kale and water; cook, stirring, until bright green and wilted, about 2 minutes. Stir in chicken, cumin, salt and pepper; cook for 1 minute more. Transfer to a large bowl.
Combine enchilada sauce, sour cream and chipotles to taste in a small bowl. Spread ½ cup of the mixture in the pan. Place 4 tortillas over the sauce, overlapping them to cover the bottom. Top with half the chicken mixture, ¼ cup onion and ½ cup cheese. Layer on half the remaining sauce, 4 tortillas, the remaining chicken, ¼ cup onion and ½ cup cheese. Top with the remaining tortillas, sauce and cheese.
Bake the enchiladas until bubbling, 12 to 15 minutes. Sprinkle with the remaining ¼ cup onion before serving.
