Place 1/4 cup buttermilk or half-and-half and 2 large eggs in a medium bowl and whisk to combine. Place 2 cups panko breadcrumbs, 2 teaspoons garlic powder, 2 teaspoons onion powder, 1 1/2 teaspoons kosher salt, 1 1/2 teaspoons mustard powder, and 1/2 to 1 teaspoon black pepper in second bowl or shallow dish and whisk to combine.
Place 1/4 cup cornstarch on a rimmed baking sheet. Pat 1 1/2 pounds chicken tenders dry with paper towels. Place on the cornstarch and toss until fully coated. Working in batches, dip the chicken in the buttermilk mixture, then dredge in the panko mixture until fully coated. Return to the baking sheet in a single layer. Let rest at room temperature for 30 minutes, which gives the coating time to adhere to the chicken.
Heat an air fryer to 400ºF. Coat both sides of the chicken with cooking spray. Working in batches as needed, arrange the chicken in a single layer in the air fryer basket. Air fry, flipping halfway through, until cooked through, golden-brown, and crispy, 10 to 12 minutes total. Serve with your favorite dipping sauce.