Brush the pepper halves with a little of the olive oil, place on a grill pan and place under a preheated grill for 5-8 minutes until charred. Place in a bowl, cover tightly with clingfilm and leave to steam for 5 minutes; peel off the skins and finely chop the peppers.
Heat 1 tbsp of the oil in a pan, add the red onion, garlic and chilli, and cook for 3-4 minutes