Slice tomatoes about 1/4 inch thick, using a bread knife for even cutting. Mix egg, milk, garlic powder and cayenne and set aside
Salt and pepper the tomatoes and let rest a bit on a rack before dredging in the flour (or you can put the S & P directly in the flour)
Dip a tomato slice in the flour, then in the egg mixture and then in the Panko bread crumbs. Repeat with other slices and place on an elevated cookie cooling rack.
Add about a 1/2 inch-1 inch of oil (give or take, you just want the tomato slices to be completely covered in oil when frying) to a cast iron skillet (or any heavy skillet) on a medium to high heat.
Fry the tomato slices turning as needed just until turning a light brown. (remember you are only frying the coating as the tomatoes are fine just as they are)
Drain the tomato slices on a rack over paper towels and immediately sprinkle with Parmesan cheese. (OPTIONAL: I then stand my slices up in a large colander to keep them from being soggy)
Serve with buttermilk ranch or your preferred dipping sauce.