Preheat oven to 375* F
Place cauliflower, carrot and onion onto an unlined sheet pan. Sprinkle coriander and cumin over the veggies, followed by a pinch of salt and plenty of cracked black pepper. Drizzle the veggies with 2 tablespoons of olive oil and toss well to coat everything. Roast in a 375* oven for 45 minutes or until the veggies are soft and beginning to brown.
Meanwhile, combine lentils and 3 cups of vegetable stock into a 2 quart pot. Bring to a boil, reduce heat to simmer and cook until lentils are completely soft, about 15 minutes.
Combine roasted veggies and red lentils in your blender with the remaining tablespoon of olive oil and 1 additional cup of vegetable stock. Blend until completely smooth, adding the last remaining cup of vegetable stock if you prefer a runnier soup.
Return to the pot to warm through and serve.
Or portion into containers and freeze for up to 1 month.