Tip the rice into a large bowl and cover with cold water. Whisk for 1-2 mins till the water goes cloudy. Drain and rinse under cold water.
Tip the rice into a small pan. Add 400 ml boiling water and a pinch of salt. Cover. Bring the pan to the boil. Turn the heat right down and gently simmer the rice for 25 mins till it’s tender and the water is absorbed. Take off the heat. Set aside, lid on, for 5 mins to finish cooking the rice.
Peel and chop the onion. Peel and finely slice the garlic. Trim and chop the rhubarb into 2 cm pieces. Heat a deep frying pan or wok and add 1 tbsp olive oil. Add the onion and garlic. Stir and fry for 4 mins till soft and glossy.
Add 2 tsp garam masala to the onions and cook for 2 mins. Add 1 tsp turmeric. Tip in the red lentils and stir thoroughly to coat in the spiced onions.
Pour in 150 ml boiling water and stir for 3 mins till absorbed. Add the rhubarb with another 150ml boiling water. Add 1 tbsp sugar. Stir and cook for 10 mins till the rhubarb is just soft and the lentils are cooked through.
Grate or pare the zest from the lemon. Stir into the yogurt. Juice one half and slice the other half into wedges to serve. Pour the juice into the lentils. Stir the spinach through the
lentils to just wilt it.
Roughly chop the coriander leaves. Stir half of the chopped coriander through the lentils, saving the rest for later. Fluff up the rice with a fork.
Serve the lentil and rhubarb curry with the rice. Top with a dollop of yogurt and a scattering of the remaining coriander leaves. Pop a lemon wedge on the side for squeezing.