Peel and finely chop the onion. Peel and grate or crush the garlic. Break the spaghetti into small lengths, around 2-3cm long. Crumble the stock cube into a heatproof jug and stir in 450ml boiling water to dissolve it. Tip the quinoa into a sieve and give it a good rinse for 1-2 mins.
Put a medium pan over a medium heat for 1 min. Add ½ tbsp oil and the spaghetti. Gently fry for 2-3 mins, stirring occasionally, till the spaghetti is browned all over.
Add the onion to the pan with 2 tbsp water. Season with a pinch of salt and pepper. Cook, stirring a few times, for 5 mins till the onion is soft and has picked up a little colour.
Stir in the garlic with 1 tsp cumin seeds. Cook and stir for 1 min, then add the quinoa. Cook and stir for another 1 min.
Pour in the vegetable stock. Pop a lid on the pan, turn up the heat and bring to the boil. Once it's boiling, turn the heat down and simmer for 12-15 mins, stirring occasionally, till all the water has been absorbed.
While the pilaf simmers, snap the woody ends off the asparagus spears (the spears will bend and snap at the right spot). Halve the spears. Roughly chop the cashews. Finely chop the mint leaves. Finely grate the zest from the lemon.
Warm a dry frying pan over a medium heat. Add the asparagus and dry fry for 5 mins, stirring occasionally, till browned and tender. Scoop out of the pan. Add the cashews and toast for 2 mins, till browned. Take off the heat and set aside.
When the quinoa pilaf is tender and all the water has been absorbed, take it off the heat. Add a squeeze of lemon juice and most of the chopped mint. Fluff with a fork, taste and add a pinch more salt and pepper if you think it needs it.
Spoon the pilaf into 2 warm bowls. Top it with the asparagus, cashews and spoonfuls of yogurt. Scatter over the last of the mint and the lemon zest to garnish. Serve straight away.