Peel and finely chop the onion. Warm a medium pan on a medium heat for 1 min, then add 1/2 tbsp oil and the onion. Season with a pinch of salt and fry for 8 mins, stirring every so often, till the onion starts to soften and pick up a little colour.
While the onion fries, peel and grate or crush the garlic. Peel and grate the ginger. Stir the garlic and ginger into the onion with 2 tbsp tikka masala spice mix and 1 tsp turmeric. Cook, stirring well, for 1 min.
Tip the lentils into the pan and give them a stir to mix them in with the spiced onion. Pour in the cherry tomato passata and the coconut milk (give the tin a good shake before you add it to try and mix the cream back into the milk – but don’t worry if they’ve separated, it will all come together in the pan). Bring to the boil, then turn the heat down and pop on a lid. Simmer for 15 mins, stirring a few times to stop the curry from sticking, till the lentils are tender and the curry has thickened.
While the curry simmers, rinse the rice under cold water and tip it into a small pan. Add 300ml boiling water and a pinch of salt. Cover, bring to the boil and then turn the heat right down. Very gently cook the rice for 8-10 mins till all the water has been absorbed. Take off the heat and leave the rice to steam in the pan, lid on, for 5 mins to finish cooking the rice.
While the rice cooks, trim the dry ends off the cavolo nero and then finely slice it. Finely slice the chilli, flicking out the seeds for less heat.
When the lentil curry has thickened, fork the cavolo nero into it. Simmer for 4-5 mins, lid off, to just wilt the cavolo nero.
While the cavolo nero cooks, warm ½ tbsp oil in a frying pan. Add the chilli, curry leaves, and 2 tsp each cumin seeds and black mustard seeds and sizzle for 30 secs-1 min till the chilli and spices smell aromatic and are crisp. Take off the heat.
Fluff the rice up with a fork and spoon into 2 warm bowls. Top with the curry and spoon over the fried spices to finish the dish. Serve straight away.