To make the vinaigrette: Well in advance, cook the capsicums over direct/high heat until the skins are evenly charred on all sides, 10 to 12 minutes, turning every 3 to 4 minutes.
Remove them from the barbecue and place in a paper bag; close tightly. Let them stand for 10 to 15 minutes to steam off the skins. Remove the capsicums from the bag and peel away the charred skins. Cut off the tops and remove the seeds. Cut the capsicums into 5mm strips and set aside. In a medium bowl, whisk together the remaining vinaigrette ingredients. Add the capsicum and set aside for up to 24 hours.
Lightly brush or spray the snapper steaks with olive oil. Season them with salt and pepper to taste. Cook them over direct/medium heat
until the flesh is opaque in the centre, 2½ to 3½ minutes each side
Serve the snapper steaks with the roasted pepper vinaigrette spooned over the top.