1. Combine the beef and 2 tablespoons of the mayonnaise and marinate for at least 15 minutes.
2. Sprinkle over the cornflour and mix well.
3. Heat a little oil in a frying pan and sear the beef and red onion slices in batches until crispy and cooked medium rare.
4. Half fill a tortilla with the beef mixture, then top with a sprinkling of cheese and a few dollops of garlic mayonnaise and fold over to enclose the filling. Gently fry on each side until golden.
5. For the salsa combine all the ingredients, mix well and season to taste.
6. Serve the fried tortillas with the salsa and greens.