In a large bowl, mix together buttermilk, lemon juice, salt, and pepper.
Add in chicken, then stir to combine.
Let marinate at room temperature for 30 minutes. If you're going to marinate longer, cover the bowl with saran wrap and place it in the fridge for up to 8 hours.
Preheat oven to 425 degrees F and line a baking sheet with a silicone baking mat. Set aside.
Mix together flour and ranch seasoning on one plate.
Whisk eggs on another plate.
Mix panko and parmesan on a third plate.
Working with one chicken tenderloin at a time, fully cover the tenderloin in the flour/ranch mixture, then whisked egg, and then panko/parmesan mixture.
Place onto prepared baking sheet, then repeat with remaining tenderloins.
Spray the tops with cooking spray.
Bake in preheated oven for 15-20 minutes, or until the panko is golden-brown and the chicken is cooked through.
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