Add the beef to a medium-sized mixing bowl and sprinkle over all of the seasoning. Use your hands to combine until the seasoning is evenly dispersed. Don't squeeze the beef into oblivion otherwise it'll come out chewy - just enough to mix everything together.
Divide the meat into 4 and evenly spread it over each flatbread, ensuring you cover the entire surface and right to the outside (it will shrink).
Add a drizzle of oil in a large pan over medium-high heat. Once hot, add a flatbread meat-side-down and gently press down with a spatula. Fry for 3-4 mins, or until the beef is no longer pink and it has built up a bit of a crust (you can lift the flatbread to check).
Flip the flatbread over and fry for 30 seconds to heat through and lightly toast the other side. Remove from the pan, wipe out most of the fat then add the next one in.
Stack the gyros with tzatziki, lettuce, tomato, onion, fries, more tzatziki, feta and a pinch of dill. Tuck in and enjoy!