Ideally, this recipe is a great way to utilize leftover grilled chicken. If using leftover grilled chicken, skip to step 3 to sauté onions. If not, start by seasoning chicken breast with salt and pepper to taste.
Then add only 1 tablespoon oil to sauté pan and set heat to medium-high. When pan and oil are hot, gently place chicken breast in pan. Sauté chicken until both sides are browned and internal temperature of chicken registers 165°F.Set aside to cool but reserve pan for the onions.
Place remaining oil in reserved pan and add sliced onions over medium heat, season with salt and pepper to taste. Sauté onions until they are soft and translucent. Remove from heat and set aside.
To make pesto aioli, add prepared pesto and mayonnaise in a bowl and whisk to combine.