Using a mortar and pestle, or in the bowl of a food processor, pound or pulse the ginger into a paste. Add the parsley, cilantro, lemon zest, jalapeño, saffron and mash or pulse to combine. Slowly pour in the olive oil in a steady stream while blending to form an emulsion. Transfer the sauce to a bowl and stir in the lemon juice. Season with salt, cover and place in the fridge for at least 2 hours before serving so that the flavors can meld.