Whisk olive oil, white balsamic vinegar, salt, and pepper together to make the vinaigrette. Set aside.
In a bowl, gently toss diced avocado, mango, grilled chicken, and red onion until combined.
Arrange the baby red butter lettuce on a large platter or divide evenly onto 4 plates.
Top the lettuce with the chicken and avocado mixture and drizzle half of the vinaigrette over the salad.
Serve with remaining vinaigrette on the side for additional dressing if desired.
Notes
This fresh salad is perfect for hot days when you want a delicious meal without turning on the stove. Leftover grilled chicken can be used to speed up preparation.