Rinse the quinoa and tip into a pan. Add enough water to cover by 1 cm. Bring to the boil. Cover and cook for 10 mins till the quinoa is cooked but has a slight bite. Set aside.
Set a griddle or frying pan over a high heat. When hot, cook the squash (in batches if needed) for a few mins on each side, till nicely charred and cooked through.
Top and tail each squash, then cut into rough chunks about 2 cm thick. Chuck into a large bowl with 1 tbsp oil and some seasoning. Toss well to coat.
Zest and juice the lemon into a bowl. Finely chop the garlic clove and add to the bowl with 1 tsp of the mustard. Stir in 2 tbsp oil and season well.
Peel the apple and chop into small chunks about 1 cm in size.
Layer the rocket, quinoa, griddled squash and apple on plates, then drizzle over the dressing. Serve immediately.