Heat 1 tbsp sunflower oil in a medium-sized saucepan over medium-high heat.
Finely chop 1 onion and fry for 3-4 minutes, stirring frequently.
Toast and crush 1 tsp whole cumin seeds and 1 tsp whole coriander seeds in a small mortar and pestle. Add them to the cooked onion along with the 1 tbsp garam masala, 1/2 tsp ground turmeric, 2 cm fresh ginger root, grated, and 3 garlic cloves, finely chopped. Season to taste with Shetland sea salt and freshly ground black pepper. Fry for another minute or so.
Add 400 grams tinned plum tomatoes and 1 tbsp tomato puree and bring to a gentle simmer.
Add 750 grams butternut squash, peeled and cubed, and stir to coat well.
Simmer gently for 40 minutes.
Rinse and drain 400 gram tinned chickpeas and add to the pot. Check the squash's tenderness. Simmer for 10-20 minutes more, depending on whether your squash needs more or less time.
Serve with a spoonful of low-fat yoghurt, fresh coriander leaves and a squeeze of lemon juice.