Heat 1 tbsp of oil in a large lidded pan over a medium heat and cook the onion for 10 minutes until soft, without browning, then add the diced squash and garlic. Cook for 8-10 minutes until softening at the edges. Add the spices, coat everything well, stirring for a minute or so. Season generously, then add in the passata, sugar and 250ml of water. Stir, cover with a lid, reduce the heat and cook gently for 20-25 minutes (stirring occasionally and adding a splash of water if it begins to look a little dry) or until the squash has cooked through.