Heat the oven up to 180º. Wash and dry all the ingredients. Put the peppers, aubergines, tomatoes and onions (all whole) in an oven dish or on the oven tray. Put them in the oven. Wrap the potatoes up in foil and put them in the oven too. Leave for approximately one and a half hours to roast. Turn them over once.
When they are roasted, take the vegetables out and peel all of them (except the potatoes). Some people find it easier to peel red peppers by hand. It is importante to peel them as soon as they are taken out of the oven - if they are left too long to cool, the skin may cling onto the peppers. Cut the tops off the aubergines and red peppers.
Remove the little pips from inside the red peppers, and cut the peppers and aubergines into long strips. Slice the onion and tomato. Keep all ingredients separate and add salt, pepper, a few drops of vinager and a generous amount of olive oil.
Cut the baked potatoes, empty the skins, cut them up, add olive oil and salt and pepper.
Put all the ingredients on a serving dish (don't mix them up - make individual portions of each vegetable). Sprinkle the chopped garlic over the whole dish, season with salt and pepper (and ground cumin or whole cumin seeds if you wish) and pour some more olive oil and vinager over if required.