Preheat the oven to 220°C/gas mark 7. Blitz the cauliflower in a food processor until you have rice-like shards.
Finely chop the spring onions and put them into a pan with a little coconut oil or ghee. Fry for a couple of minutes, until beginning to brown. Add the chopped chilli and garlic, then the spices and curry leaves and cook for another 2 minutes. Add the cauliflower, spinach, coriander, a squeeze of lemon and a good pinch of salt and cook for 5 minutes, then lay the mixture on a tray to cool down quickly.
Melt the coconut oil or ghee and have this ready along with a pastry brush. Remove your filo pastry from the packet and keep under a damp cloth or tea towel to stop it from drying out.
Lay one sheet of the pastry on a clean, dry work surface and cut it lengthways into three long equal pieces. Put 1 heaped tsp of the cauliflower mixture on the bottom left of the pastry then fold the right-hand corner over the mixture to create a triangle shape. Continue folding, keeping the triangle shape, and brushing a little oil in-between each fold. You should then have a nicely triangular-shaped samosa. Give it a final brush with oil and sprinkle with the nigella seeds.
Repeat with the rest of the pastry and the mixture. Bake in the oven for 15 minutes.
Meanwhile, make a quick mango chutney. With the skin still on, cut off the cheeks of each mango, leaving the stone behind. Carefully slice into the cheek, almost all the way into the skin, in 1cm strips, and then across to make 1cm squares. Push from the skin side to flip the mango into a hedgehog, and use a spoon to scrape off the roughly 1cm pieces of flesh.
In a small saucepan, toast the spices, then add the mango and lime juice and vinegar. Cook for 5 minutes until the mango has started to break down, then take off the heat. Serve with the samosas.