Squeeze the juice of half a lemon into a larger bowl. Peel and finely chop the garlic and onion and add to the juice. Add the cinnamon, fennel, cumin, oregano, pepper and salt, mix everything together and top up with a little olive oil. Cut the cold-washed, dried meat into approx. 3 cm cubes and add to the marinade. Now maybe pour in enough olive oil that the meat doesn't look out. Stir everything well, mix, cover and put in the fridge for a few hours (ideally overnight) to marinate.
For the skewers, wash the whole lemon with hot water, dry it and quarter it lengthways and cut the quarters into approx. 0.5 mm thick slices. Peel the red onion, cut into eighths and peel apart in two layers. Then skewer meat, lemon slice, 2 onion slices, meat ... alternately on 4 metal skewers (approx. 20 cm long). At the other end, the meat should finish off. About 6 pieces fit. on it. It does not have to be dabbed off after it has been removed from the marinade. Do not throw away the leftover marinade, but keep it for the shepherd's salad.
Ideally, fry the skewers either on the grill or in a grill pan until they have turned well. Inside, however, the meat should still be light pink. If you don't have a grill or grill pan, you can of course fry the skewers in a conventional pan. Be careful with additional frying fat, as the marinade makes the skewers very oily.