In a medium bowl, combine the flour, garlic powder, onion powder, paprika, salt, and pepper.
In another medium bowl, whisk together the buttermilk and egg.
Dredge each cube steak in the flour mixture, then dip it into the buttermilk mixture, and finally dredge it again in the flour mixture, pressing the flour onto the steak to ensure a good coating.
Heat about 1/4 inch of oil in a large cast iron skillet over medium-high heat.
Fry the steaks in batches until golden brown and cooked through, about 3-4 minutes per side. Drain on paper towels.
Spread mayonnaise on the bottom half of each toasted bun.
Place the lettuce and a slice of tomato on the bun, then one of the pieces of chicken fried steak.
Spoon a generous amount of cream gravy over the steak. Cover with the top half of the bun and serve with your favorite sides.