Preheat your oven to 180C / Fan 160C / Gas 5.
Trim and peel the red onions and cut into wedges. Scrub the beetroot and slice it into thin rounds. Trim the spring onions and cut each into 4 pieces. Drain the chickpeas and shake dry.
Divide the onions, beetroot, spring onions and chickpeas between two roasting tins and toss each with 1 tbsp oil and a good pinch of salt and pepper. Slide into the oven and cook for 25 mins, turning halfway.
Grate the lemon zest into a bowl and squeeze in the juice. Sprinkle in the sumach, black onion seeds, a little salt and pepper and stir in 1 tbsp oil.
Scatter the spinach into a bowl and fold in the roasted vegetables and chickpeas. Tumble with the dressing and torn basil leaves and serve.