Soak 18 wooden skewers in cold water for at least 30 minutes to prevent scorching. Slice the beef into long, ½cm (¼in)-thick slices. Combine the garlic, red onion, chilli, ginger, lime zest, soy sauce and sugar. Add the beef, mix, then cover and chill for at least 30 minutes (or up to 12 hours). After marinating, thread the beef onto the skewers and set aside. Reserve the marinade. For the peanut sauce, put the peanuts, red onion and sugar into a large dry frying pan and cook on a medium heat for 5 minutes, stirring, until the sugar melts. Turn up the heat and cook until the peanuts are golden. Add the garlic, ginger and chilli and cook for a minute. Add the coconut milk, soy sauce and 450ml (¾pt) cold water. Simmer on a low heat, stirring occasionally, for about 20 minutes or until thickened. Stir in the lime juice and season to taste. Whizz in a blender until you have a paste. Preheat a dry griddle pan over a high heat or heat a barbecue to medium heat. Cook the beef skewers, brushing occasionally with the reserved marinade, for 2-3 minutes each side or until beginning to char at the edges and cooked through. Scatter with coriander leaves and serve with lime wedges, some rice or grain salad and prawn crackers, if you like.