Sweat the aromatics (optional but recommended): In a frying pan, heat the olive oil over a medium heat. Add the onion, carrots, and celery, and cook for 5-7 minutes, stirring occasionally, until the onions are translucent and the mixture smells sweet and fragrant. The carrots should begin to soften and look a little glossy. This step deepens the flavour, but if you are in a real rush, you can skip it and add everything raw to the slow cooker.

Bloom the spices: Add the minced garlic, dried thyme, cumin, and smoked paprika to the pan. Stir for another minute until the kitchen smells wonderfully aromatic. The garlic should be fragrant but not burning.

Combine in the slow cooker: Tip the sautéed vegetable mixture into your slow cooker. Add the rinsed lentils, the can of chopped tomatoes, the vegetable stock, and the diced potatoes. Give everything a good stir so the lentils are distributed and the stock turns a rich, deep red from the tomatoes and paprika.

Cook low and slow: Place the lid on your slow cooker. Cook on LOW for 6-8 hours or on HIGH for 3-4 hours. After 3 hours on high, the lentils should be tender but still holding their shape, and the potatoes should break apart easily against the side of the pot.

Add the quick-cooking veg: About 20-30 minutes before you plan to serve, stir in the diced courgette. It will steam and soften quickly. The courgette should turn a slightly brighter green and become tender, but not mushy.

Finish with greens: Just before serving, stir through the handful of spinach or kale. The heat from the soup will wilt the leaves in about 2-3 minutes. The spinach will turn a vibrant, deep green. Taste the soup and season generously with salt and pepper. The lentils will absorb a surprising amount of salt, so do not be shy.