Preheat the oven to 200 C (400 F) and put the tomatoes cut side-up on a baking tray. Drizzle them with some olive oil and roast in the oven for 20-30 minutes until slightly shrivelled.
Meanwhile bring the water to the boil in a small pot. Add the rinsed buckwheat and stock cube, stir together and then turn down the heat to simmer. Place a lid on and leave to cook for 20 minutes then drain and place back into the pot. Cover with the lid again and leave for 10 minutes to absorb any excess moisture.
Take the apple and slice it thinly. Cut out the core and then cut the slices into matchsticks. Cut the orange in half and squeeze the juice of one half over the apple matchsticks, tossing to coat.
Squeeze the juice from the other orange half into a small jar. Add the balsamic, mustard, olive oil and salt to the jar. Fit the lid and shake the jar to emulsify the dressing.
Take a large jar with a tight-fitting lid and pour the dressing into the bottom. Layer the cooked buckwheat on top, followed by the roasted tomatoes, apple, the spinach and finally the sprouts. Seal with the lid.
To eat: pour the salad out into a bowl and toss to coat with the dressing.
- I also like to add crumbled feta to this salad, layered into the jar just after the spinach.