In a large skillet, heat oil over medium-high heat. Add tortilla strips; cook eight minutes, stirring frequently, until crisp and golden brown. Remove from skillet; set aside. In the same skillet, add chicken and onions; cook and stir over medium-high heat until chicken is no longer pink and onions are tender. Stir in taco seasoning and water; cook four minutes, stirring frequently. Meanwhile, in large bowl, gently toss salad greens, beans, and dressing. Spoon salad mixture onto individual serving plates. Place chicken over salad; sprinkle with cheese and tortilla strips.