1. Working over the sink, wrap the grated beetroot in a clean J-cloth and squeeze out as much liquid as possible. In a large bowl, mix the beetroot, spring onions, garlic, mint, lemon zest, half the lemon juice, 2 tbsp of the flour and the egg, along with a good pinch of salt and pepper. When well combined, stir in the feta.
2. Form the mixture into 4 burger-shaped patties and coat with the remaining flour. Heat a large frying pan over a medium-high heat with 3 tbsp olive oil and fry the patties for 4-5 minutes on each side until crisp on the outside and cooked through.
3. Mix the remaining oil and lemon juice with a pinch of salt and pepper and toss with the salad leaves. Serve the burgers in buns with the salad.