Place the chicken breast in a small pot and cover with water; bring to a gentle simmer and cook for 12-15 minutes until fully cooked through.
Remove the chicken from the water, let it cool slightly, and then dice it into bite-sized cubes.
While the chicken cools, slice the red grapes in half, finely dice the celery and red onion, and roughly chop the pecans.
In a medium mixing bowl, whisk together the Greek yogurt, avocado oil mayonnaise, lemon juice, sea salt, black pepper, and dried dill until smooth.
Add the diced chicken, grapes, celery, onion, and pecans to the bowl with the dressing and fold everything together until well coated.
Arrange the butter lettuce leaves on a plate and scoop the chicken salad into the center of the leaves to serve.