Preheat the oven to 200C/400F. Arrange the whole red bell peppers on a roasting pan and drizzle with 1 tbsp of olive oil. Take a large head of garlic and slice the top off to expose the cloves, place on a sheet of aluminium foil and drizzle with olive oil, wrap the garlic head in the foil and place on the same roasting pan as the peppers. Roast for 40 minutes until the peppers are soft and collapsed and the garlic cloves are very soft.
Take out of the oven, cover the peppers with a kitchen towel and cool. Once the peppers are cool enough to handle you can either peel them or leave as they are but remove the seeds. Once the garlic is cool enough to handle, squeeze the cloves out of their peels.
Meanwhile, toast the walnuts on a frying pan over low heat for about 5 minutes, stir often to avoid burning, remove from the pan and cool.
In a food processor combine the roasted red peppers, smoked paprika, sherry vinegar, olive oil, ground cumin, salt and the roasted garlic, pulse until blended.
Add the toasted walnuts and pulse briefly until it forms a paste but the walnuts still retain some texture.