Heat the olive oil in a large saucepan over medium heat. Add the finely chopped onion and cook for 4–5 minutes until soft and golden. Add the minced garlic and grated ginger and cook for another 2 minutes until fragrant. Add the ground turmeric, cumin, and coriander — stir directly into the oil and cook for 1 minute to bloom the spices.
Pour in the canned chopped tomatoes and stir well, scraping any spices from the bottom of the pan. Add the rinsed red lentils and vegetable broth. Stir everything together and bring to a gentle boil.
Add the cauliflower florets to the pan. Reduce the heat to low, cover with a lid, and simmer for 20–25 minutes, stirring occasionally, until the lentils have completely broken down and the cauliflower is tender. If the dal looks too thick, add a splash of water and stir.
Remove from heat. Stir in the lemon juice and black pepper. Taste and adjust seasoning. Divide between two bowls and scatter fresh coriander generously over the top. Serve as is or with a small portion of brown rice.