Often, one ingredient in a dish will do a lot of heavy lifting, either boosting flavour or allowing other ingredients to shine. In this recipe, dijon mustard is not a dominant flavour, but it is the sun around which orzo, onions, lemon and cauliflower revolve. You’ll need a 25cm x 30cm (or thereabouts) baking dish for the orzo and a large oven tray (or two smaller ones) for roasting the cauliflower