Place bell peppers in a baking tray and roast at preheated 180 C oven for 20 minutes. Remove and using tongs, give peppers a half turn. Return to oven roast for another 20 minutes. You know it's done when the skin is blistered and lightly charred. Leave to cool, then remove skins and chop bell peppers into strips.
In the meantime, fill up a pot with enough water to cover potatoes and boil for 40 minutes or until potatoes are soft but not crumbly. Remove and leave to cool, then remove skins and dice into bite-sized chunks.
In a mixing bowl, place all dressing ingredients and whisk until smooth.
Add in potatoes, roast peppers, fried shallots and spring onions and toss to coat with dressing. Serve!