Preheat the oven to 425°F. Set out a large baking sheet.
Make the spice blend. In a small bowl, combine the turmeric, cumin, ground chillies, coriander, cinnamon, fenugreek, and fennel seeds. Stir to combine and set aside.
Place all of the cauliflower florets on the baking sheet. Drizzle with 2 tablespoons of the oil, half of the spice blend, and some salt and pepper. Toss to coat the florets in the oil in spices. Arrange the cauliflower in a single layer and slide the baking sheet into the oven. Roast the cauliflower until deeply caramelized, about 40 minutes, flipping and toss the florets at the halfway point.
Add the crushed tomatoes, coconut milk, and vegetable stock to the skillet and stir again. Bring this up to a boil and then simmer until the lentils are totally soft and starting to break up, about 25 minutes, stirring often. If the lentils seem to be sucking up too much liquid, just keep adding more splashes of vegetable stock (or coconut milk if you want to go a bit richer).
Once it's done, season generously with salt and pepper and add the lime juice. At this point, you can use an upright blender to blend the sauce OR you can leave it as is. I prefer to blend it for 1 full minute until itās completely smooth.