Heat your oven to 180°C /Fan 160°C/Gas 4. Crumble the stock cube into a heatproof jug and mix with 350ml boiling water. Tip the buckwheat into a pan and cover with the stock. Simmer for 15 mins till tender, then drain.
While the buckwheat cooks, arrange the cherry tomatoes on a baking tray. Toss with 1 tbsp olive oil and a sprinkle of salt and pepper. Roast in the hot oven for 15 mins.
Heat a large frying pan over a medium heat for 1 min. Sprinkle in 1 tsp cumin seeds and toast for 2-3 minutes, then tip them into a bowl.
Pour 2 tbsp oil into the frying pan and add the buckwheat. Fry for 5 mins, stirring frequently, till crispy. Stir in most of the toasted cumin seeds and season well.
Trim the asparagus (see our tip). Add to the roasting tray with the tomatoes. Roast for a further 5 mins.
Spoon the yogurt into a bowl and fold in the saffron powder, the juice from half the lemon and a little salt and pepper. Cut the remaining lemon into wedges.
Heap the buckwheat onto each plate. Arrange the asparagus on top and serve with the cherry tomatoes and dollops of the saffron yoghurt. Scatter over the remaining toasted cumin seeds and squeeze over the lemon wedges.