In a medium bowl, whisk the eggs and buttermilk. Add the raw shrimp and sliced red pepper. Stir to coat.
On a large plate, mix together the flour, cornstarch, paprika, garlic powder, onion powder, salt, and pepper.
One piece at a time, dip the shrimp and peppers from the wet mixture into the dry mixture. Shake off any excess, then place them on a cooling rack set over a sheet pan. Let them rest for 2–3 minutes to help the coating stick.
Heat oil in a large skillet to 325°F. Use a thermometer for best accuracy.
Add the shrimp and peppers in a single layer. Fry for about 2 minutes per side, or until golden and crisp. Don’t overcrowd the pan.
Transfer to a plate. Sprinkle with fresh parsley and flaky sea salt. Add lemon if desired. Serve immediately.