Pour oil in skillet and warm to medium heat. (About a half inch of oil.)
Lightly salt and pepper both sides of tomatoes.
Mix flour and garlic powder in a shallow dish.
In another shallow dish, beat eggs with buttermilk.
In a third dish, combine bread crumbs with cayenne.
Dredge tomatoes through the flour, then the eggs, and then the bread crumbs.
When oil is hot, add a few pieces at a time. Don't crowd them. Cook about 2-3 minutes. Drain on paper towels. Sprinkle with Parmesan and chopped green onions (optional).
Serve with your favorite dipping sauce, but they don't really need anything else...