Toast almonds in a dry skillet over medium heat until fragrant, 3–4 minutes. Transfer to a plate to cool.
Whisk yogurt, mayonnaise, lemon juice, Dijon, olive oil, garlic powder, salt, and pepper in a large bowl.
Add chicken, celery, red onion, grapes, dill, and cooled almonds to the bowl.
Fold everything together until the chicken is evenly coated in the dressing.
Chill 10–15 minutes to let the flavors meld, then taste and adjust seasoning.