Soak eight wooden skewers in cold water for 15 minutes. This will prevent them burning during cooking.
Slice the steak lengthways as thinly as possible and set aside in a bowl.
Put the oil, lemon rind, lemon juice, chillies, coriander and salt into a food processor. Blitz to a smooth paste, then add the paste to the bowl of steak pieces. Mix well, then cover and set aside for 20 minutes.
Meanwhile, make the salad. Put the garlic, onion, coriander, chilli, mustard and oil into a bowl and mix well. Add the lentils and chickpeas. Squeeze in the lime juice and mix through the salt, then cover and set aside.
Preheat the oven to 240°C/220°C fan/gas 9 and lightly grease a roasting dish. Or if you prefer to cook your skewers on a griddle pan, grease it lightly and put it on a medium to high heat to start warming up.
Meanwhile, skewer the beef pieces in a zigzag pattern. Do this until you have filled all eight skewers. If you have any leftover marinade, just dab it on top of the beef.
Line the skewers on to the greased roasting dish and bake for eight to 10 minutes, making sure to turn them over halfway through. Or, if griddling, put them on the hot pan and cook for three to four minutes on each side.
Once cooked, serve the warm beef skewers with the salad alongside.