Put the mince in a large mixing bowl. Add the spices, then season with salt &pepper. Combine well and make four balls. Then flatten these slightly between your palms. Put them on a plate and rest until you’re ready to cook them.
Peel then cut the onion into thin rings. Heat some oil in a frying pan and gently soften the onion (under cover) for about 10 minutes. Set aside.
Cut the avocado in half and scoop the flesh into a small mixing bowl - add the spring onion and coriander and the lime juice. Deseed and chop the chilli (if used) and mix into the avocado cream. Season to your liking and set aside.
Grill or toast 4 buns (cut in half) and set aside.
Heat a griddle pan, BBQ or frying pan. Brush the burgers with some oil, then fry them for 3-5 minutes on each side to your liking.
Assemble the burger: put a piece of lettuce on the bottom half of the bun, then add some some avocado cream. Place the burger on the avocado, then top with soured cream and fried onion. Sprinkle with some paprika, put the top half of the bun on and serve.