Heat oil in large skillet or wok over medium-high heat until hot. Add chicken strips and onion; cook and stir 4 to 6 minutes or until chicken is no longer pink. Add seasoning mix and water; cook and stir about 6 minutes or until sauce is bubbly and thickened. Remove from heat.
Line 4 salad bowls or plates with lettuce. Spoon chicken mixture onto lettuce. Top with cheese, olives and avocado. Garnish with sour cream and salsa.