Fill your kettle and boil it. Tip the couscous into a heatproof bowl and pour in 150ml boiling water from the kettle. Stir, cover the bowl with a plate and set aside to soak for 10 mins. The couscous will absorb the water and become tender.
Meanwhile, peel and grate the garlic into a small bowl. Grate in the lemon zest and squeeze in the juice. Add 1 tsp Dijon mustard and 1 tbsp olive oil. Season with a pinch of salt and pepper and stir into a dressing. Set to one side.
Peel the red onion and thinly slice it. Peel the carrot and beetroot (see our tip below) and chop both into matchsticks. Slice the tomatoes into small chunks. Halve the avocado and scoop out the stone. Slice the avocado into thin pieces. Toss the veg together in a large salad bowl.
Pick the mint leaves and roughly shred them. Add the mint to the veg and add the mung bean sprouts. Pour over the dressing and toss together.
Fluff the couscous with a fork and divide it between a couple of plates. Top with the dressed salad and serve.