Preheat the grill and set the tray at about 15cm from the heat source. Line a baking tray with aluminium foil.
Cut the capsicums in half from top to bottom; remove the stem, seeds and ribs, then place the capsicums cut-side-down onto the prepared baking tray.
Cook under the preheated grill until the skin of the capsicums has blackened and blistered, about 5 minutes. Place the blackened capsicums into a bowl and tightly seal with cling wrap. Allow the capsicums to steam as they cool, about 20 minutes. Once cool, remove the skins and discard.
Transfer the roasted capsicums to a blender or food processor. Add the red wine vinegar, olive oil and salt; process until smooth.