Heat the oven on grill and move the rack to the upper third.
Slice the bell peppers into quarters, discarding the core and cutting out any white veins.
Rub them with a little olive oil and place on a baking tray.
Grill in the oven, until skins are very charred and flesh is softened, about 15 minutes.
Transfer bell peppers to a bowl and cover tightly with cling-film so they can steam.
When cool enough to handle, peel and discard the skins.
Lightly toast walnuts in a dry pan.
Keep a small handful (about 20g) aside to crumble on top of the dip before serving.
Stir in all the spices, and cook for another minute, while stirring constantly until very fragrant.
Pour in the tinned tomatoes and sugar.
Increase the heat to a simmer.
Add the chickpeas and cook, maintaining a gentle simmer, for about 10-15 minutes, allowing the flavours to develop and the sauce to thicken.
Pulse bell peppers, toasted walnuts, breadcrumbs, Aleppo pepper, lemon juice, tahini, paprika, pomegranate molasses and olive oil in a food processor until mostly smooth.
Season muhammara lightly with salt.
Plate in a shallow bowl and finish with reserved crumbled walnuts, a drizzle of olive oil and a pinch of Aleppo pepper.