BLEND broth, 1/4 cup dressing, cilantro, nuts and chile in blender until smooth.
HEAT remaining dressing in large nonstick skillet on medium-high heat. Stir in onions; cook 5 min., stirring occasionally. Add chicken; cook 2 min. on each side or until browned on both sides. Stir in mushrooms; cook 5 min. or until liquid is evaporated, stirring occasionally.
STIR in broth mixture; cover. Cook 10 min. or until chicken is done (165°F). Serve over rice; top with sour cream.