Mash one avocado in a bowl until smooth. Dice the second and set aside.
Stir yogurt, lime juice, cumin, salt, and pepper into the mashed avocado.
Add chicken, red onion, cilantro, and serrano. Mix.
Fold in the diced avocado last.
To serve: sourdough toast, lettuce cups, a tortilla, or straight from the bowl. Finish with extra lime.