In a large skillet with a tight fitting lid, bring 1-2 inches salted water to a boil (should be enough to cover the chicken). Add chicken, cover; reduce heat to medium-low. Simmer 5 minutes; remove skillet from heat. Let chicken steam, covered, until opaque throughout, 12 - 14 minutes. Transfer chicken to a medium bowl; shred with two forks. Set aside.
While chicken is cooking, make sauce. In a medium saucepan add heat oil over medium heat. Add garlic; cook until fragrant (1 min). Add flour, cumin, and chipotles; cook, whisking 1 min. Whisk in broth and 1/2 water; bring to a boil. Reduce to simmer and cook, whisking occasionally, until sauce thickened slightly, 5 - 8 minutes. Season with salt & pepper. Transfer 1 cup sauce to bowl with chicken; toss to combine
Preheat oven to 400 deg. Pour 1/4 cup of sauce into bottom of 8" square baking dish; set aside. Stack tortillas and wrap in double layer of damp paper towls; microwave until hot, about 1 min. Fill each tortilla with chicken mixture; roll up tightly, and arrange seam side down in baking dish. Cover with remaining sauce and top with cheese. Bake until hot and bubbling. 15 - 20 minutes. Let cool 5 minutes before serving.