Heat your oven to 200°C/Fan 180°C/Gas 6. Rinse the pearl barley under cold water. Tip the barley into a pan and pour over boiling water till it’s 1 cm above the barley. Cover and simmer for 30 mins till tender (keep your eye on the pan and add more water if the barley starts to dry out).
Tip 2 tsp sunflower seeds into a dry frying pan. Toast over a medium heat for 2-3 mins, shaking the pan, till golden and nutty smelling. Tip into a bowl.
Peel and slice the beetroot, Chioggia and fennel as thinly as you can – use a mandoline or the slicing attachment on a food processor if you have one. Place half the sliced veg in a bowl. Squeeze over the juice from half an orange (keep the other half for later). Add a pinch of salt and toss together.
Place the remaining sliced beetroot, Chioggia and fennel on a baking tray lined with baking paper. Drizzle with 1 tsp oil. Roast for 10-15 mins till the veg has softened and is beginning to char at the edges.
Cut the ends from the remaining whole orange so it stands up on your board. Slice the skin off, removing as much pith as possible. Cut the peeled orange into thin slices.
Tip half the watercress into a food processor. Squeeze in the juice from the remaining orange half. Pour in 4 tbsp cold water. Add a pinch of salt. Whizz together. No processor? Finely chop the watercress and whisk with the orange juice and water.
Drain the pearl barley and briefly rinse under cold water. Return to the pan and mix in half of the watercress dressing.
Arrange the remaining watercress on a platter. Top with the barley. Add a few orange slices, then layer the raw beetroot, Chioggia and fennel. Finally add the cooked veg. Drizzle over the remaining watercress dressing, orange slices and scatter over the sunflower seeds to serve.