First, we need to marinade the chicken tenders. Add tenders to a gallon ziplock bag. Add buttermilk, 1/2 teaspoon salt, 1/4 teaspoon paprika, 1/8 teaspoon garlic powder, and 1/8 teaspoon cayenne powder. Seal bag and toss chicken to coat completely with spices and buttermilk. Place bag in a bowl and set in refrigerator for at least 1 hour and no more than 8 hours.
Once chicken is done marinating, prepare the oil for frying. Place 2-3 cups of oil into a cast-iron skillet (should fill skillet halfway). heat over medium heat. The oil should take about 7-10 minutes to get hot.
While oil gets hot, prepare the dredge. Add flour, 1/2 teaspoon salt, 1/2 teaspoon pepper, 1/2 teaspoon paprika, 3/8 teaspoon garlic powder, and baking powder to a shallow dish. Whisk to combine ingredients.
Remove tenders from the refrigerator. Remove on tender from the bag and shake off excess buttermilk. Drop into flour mixture and toss with flour mixture to cover all edges of the tenderloin. Place tenderloin on a clean plate and repeat with rest of the tenderloins.
Once oil is hot, place a tenderloin into oil. If it's sizzling, then oil is hot enough. Add 3 more tenderloins and cook all 4 tenderloins for 3 minutes. Flip and cook for 2 more minutes, or until they're golden brown. Remove from oil and drain on paper towels. Repeat with any remaining tenderloins. Let tenderloins cool.
Cut cooled chicken tenders into 1 inch cubes. Set aside.