Crush garlic to a paste with sea salt and add to the chicken pieces in a bowl.
Add lemon juice, pepper, and olive oil to the chicken and marinate for at least 30 minutes.
Preheat the grill to hot and remove seeds and ribs from the red peppers.
Grill pepper quarters skin-side up for 10-12 minutes until blackened.
Steam peppers in a sealed bag, then peel and discard the skins once cooled.
Toast hazelnuts in a 200°C oven for five minutes.
Rub skins off toasted nuts and repeat the process for almonds.
Fry bread in 30ml of olive oil with sliced garlic until golden-brown.
Add nuts, peppers, raw garlic, paprika, and cayenne to a food processor.
Add fried bread, fried garlic, and red wine vinegar to the processor.
Process into a paste while gradually adding 60ml of water and remaining oil.
Preheat the grill and cut spring onions into 3cm lengths.
Thread chicken and spring onions onto skewers and grill for 12 minutes.
Serve chicken skewers immediately with the romesco sauce.