Add all ingredients into a jar with a tight fitting lid then shake to combine. Can be made ahead of time.
For the Grilled Chicken Salad:
Preheat grill to 400 degrees (medium-high for a gas grill). Meanwhile, add chicken breasts, pesto, and a big pinch of salt to a Ziplock bag then squish to coat. Allow chicken to marinate while grill is preheating.
Once grill is hot, spray both sides of each chicken breast with nonstick spray then grill for 3-4 minutes a side or until cooked through. Remove to a cutting board then let rest for at least 5 minutes before slicing. Add sweet corn cobs to the grill at the same time as the chicken then grill, rotating often, until kernels are softened and slightly charred, 8-10 minutes total. Slice kernels off the cob.
Arrange lettuce on a platter (or on plates/in bowls) then arrange grilled chicken, corn, tomatoes, red onion, and avocado on top. Drizzle with prepared vinaigrette then serve.