In a large skillet, heat butter over medium heat until melted. Stir in flour, cook for 1 minute and whisk in chicken broth. Continue stirring until smooth and thickened-- about 2-3 minutes.
Stir chipotle chili powder, salt, oregano, green chiles and black olives into the sauce and place chicken breasts into pan. Bring to a simmer, reduce heat to low, cover and cook about 15 minutes or until chicken is cooked through.
Remove chicken from pan, leaving the heat on low, and place chicken on a plate to shred into bite-sized pieces.
Stir sour cream into the sauce and return chicken to the pan along with the tortillas. Stir until combined and top with grated cheese. Cover pan and cook for 5-8 minutes until bubbly and the cheese is melted.