Whisk together buttermilk, pepper, salt, paprika, and cayenne pepper.

Add chicken tenders to buttermilk mixture. Cover and refrigerate for 4 hours, up to overnight.

Place oats in blender. Blend on high speed to produce oat flour.

Mix oat flour, potato starch, and baking powder together in small bowl.

Remove chicken tenders from buttermilk mixture. Do not discard buttermilk mixture.

Whisk oat flour mixture into buttermilk mixture to form a smooth batter.

Return chicken tenders to oat batter and coat each piece thoroughly with batter.

Heat 1 inch of vegetable oil to 340°F in a large deep skillet.

In batches, carefully lower battered tenders into pan.

Fry until golden brown, turning once, until an instant-read thermometer inserted in the thickest part of each piece registers 165°F, about 5 minutes.

Drain chicken on paper towels. Keep warm in a low oven while you fry remaining chicken tenders.