Preheat the oven to 200 °C (390 °F). Toss whole red peppers in a little olive until lightly covered. Arrange on a foil-lined, large baking tray and place in the oven, just a little higher than middle oven shelf so that the pepper’s skin is closer to the grill element.
Roast for 50-60 minutes until the skin blackens, wrinkles and blisters on all sides and the peppers collapse. I usually turn them over halfway through. The time will depend on the size of the peppers.
Meanwhile, mix the sliced onions with the rest of the ingredients and set aside to pickle slightly.
Remove cooked peppers and let them cool down for 20 minutes before peeling the skin off. The peel should slip right off but hold the peppers by the tails as they will be quite slippery. Slice peeled peppers in half, remove the core and scrape off the seeds with a knife. Then slice into thinner strips and toss with pickled onions and all of the flavoured dressing.