Preheat your oven to 180°C/160°C/Gas 5. Peel and thinly slice the onions, keeping them separate. Scoop half of the onions into a bowl and set aside for later. Peel the garlic cloves and ginger and finely grate both of them. Halve the chilli, flicking out the seeds and membrane for less heat, and finely chop. Scrub the sweet potatoes and cut into small, bite-size chunks.
Pour 1 tbsp oil into a large pan and warm to a medium heat. Slide in 1 chopped onion along with the garlic, ginger and chilli. Sprinkle in the curry leaves and 1 tbsp Bombay spice mix. Add the cinnamon stick and a pinch of salt and pepper. Fry for 5 mins, stirring frequently. If the pan begins to look dry, add a splash of cold water and stir.
Slide the chopped sweet potato into the pan, stir and continue to cook for a further 2-3 mins.
Scatter the red lentils into the pan with the veg. Crumble in the coconut cream and the stock cube. Pour in 400ml boiling water. Bring to the boil, then cover the pan with a lid and reduce to a simmer. Cook for 20 mins, stirring occasionally.
Meanwhile, peel the parsnips and cut into long batons. Scatter them into a roasting tin and add the remaining sliced onion. Spoon over 1 tbsp Bombay spice mix and add a pinch of salt and pepper and 1 tbsp oil. Toss well to combine. Slide the veg into the oven and roast for 25 mins, turning halfway.
When the curry is cooked, stir through the spinach till slightly wilted. Have a taste and add a little more salt and pepper if needed. Spoon the curry into bowls and serve with the Bombay parsnips on the side.