Melt butter in a large skillet over medium-high heat; add onions and cook 20 minutes or until tender. Reduce heat to low; add chopped chicken, roasted pepper, and cream cheese. Stir until combined; set aside.
Pulse chiles and next 5 ingredients in blender or food processor several times until combined.
Bring chile mixture and chicken broth to a boil in a saucepan over high heat; cook 5 minutes or until slightly thickened. (Mixture should be the consistency of a thin gravy.) Remove from heat and stir in salsa.
Spread one half of the chile mixture on bottom of a lightly greased 13x9 baking dish.
Spoon chicken mixture evenly down center of each tortilla; roll up and place, seam side down, in prepared baking dish. Top with remaining chile mixture, spreading to coat. Sprinkle with cheese.