In a large nonstick skillet, heat 1 tablespoon butter over medium-high heat; saute onion until tender and lightly browned, 3-5 minutes. Remove from pan., In a bowl, mix flour and seasonings; toss with chicken. In same skillet, heat remaining butter over medium-high heat. Add chicken; cook just until no longer pink, 4-6 minutes, turning occasionally., Stir in broth and onion; bring to a boil. Stir in rice. Remove from heat; let stand, covered, 5 minutes (mixture will be saucy). If desired, sprinkle with cilantro.