Wash the pearl barley thoroughly, then cover with cold water in a large saucepan. Bring to the boil, reduce the heat, then simmer for 20-40 minutes, until cooked and tender. Drain to remove any excess water and leave to cool.
While the barley cooks, add the pecan to a medium frying pan over a medium heat. Toast in the pan until fragrant and just starting to colour, then immediately transfer to a chopping board. Let cool and roughly chop, then set aside until needed.
In a jug, combine the orange juice, sherry vinegar, runny honey, garlic and mustard powder. Gradually pour in the olive oil while whisking until the dressing becomes emulsified. Season and set aside until needed.
Once cool, share the barley across four plates. Scatter over the salad leaves and drape over the butternut and parsnip. Top with the pecans and goat's cheese and dress with the orange vinaigrette, then serve.