1. In a very large bowl, combine the buttermilk, herbs, garlic, lemon juice, mustard, salt, and pepper. Add the chicken to the bowl and turn to coat in the marinade. Cover the bowl with plastic wrap and refrigerate at least 30 minutes, or up to overnight, stirring the mixture occasionally.
2. Preheat the oven to 375 degrees F. Set a wire cooking rack over a baking sheet and coat with nonstick cooking spray. Place cornflakes in a shallow dish. Remove the chicken tenders from the marinade a few at a time and dip in crumbs to coat. Arrange chicken on prepared rack. Sprinkle with any remaining crumbs and pat lightly.
3. Bake chicken for 20 minutes, or until it is no longer pink inside and the crumbs have started to brown.