Bake the peppers whole until the skins begin to blacken. Allow to cool, then remove and discard the skins and seeds.
Put the cashews in a blender and barely cover them with water. Puree into a smooth cream, adding a splash of water if it's too thick.
Dice the onion and sautee it in the oil until translucent. Add the peppers and the cashew cream. Simmer, stirring frequently, for 5-10 minutes. Add water to reach the consistency of a cream sauce, or as thick as you prefer. Season to taste. Allow to cool slightly, then blend the sauce until smooth.
Serve with pasta and/or vegetables, potatoes, whatever you like.
Source of recipe: I veganised it.