Cut the red pepper into 4 pieces, brush with oil and roast, grill or barbecue until cooked through and charred in places. Roast the garlic cloves in their skin at the same. Only 10 minutes for the garlic if being grilled or barbecued. Allow to cool.
Add all the ingredients, except the water, and blitz with the stick blender until completely smooth.
If you want a thinner sauce for drizzling then add a little of the water and blend again, add water until you get the thickness you want.