I start by combining the mayonnaise, Greek yogurt, Dijon mustard, and lemon juice in a large bowl. Then I add the garlic powder, onion powder, salt, and pepper, and whisk everything until it's smooth. Making the dressing first means it coats the chicken and vegetables evenly once everything else goes in.
Next, I add the shredded chicken, chopped celery, halved grapes, red onion, and sliced almonds straight into the bowl with the dressing. I stir gently but thoroughly, making sure every piece of chicken and every grape gets coated. This is also when I taste and adjust the seasoning if needed.
I lay the lettuce leaves out flat on a large plate or clean surface, then spoon a generous amount of the chicken salad into the center of each one. I like to fold the sides in slightly before serving so the filling stays put. Serve them right away for the best texture and crunch.