Set a large pot or Dutch oven over medium heat and let it warm for about 1 minute.

Add the olive oil to the pot.

Add the onion, carrot, celery, and 1/2 teaspoon of the salt to the pot. Cook for 6 to 8 minutes, stirring often, until the vegetables look soft and the onion is translucent.

Add the garlic and cumin to the pot. Stir for about 30 seconds, until the garlic smells fragrant.

Add the cauliflower florets to the pot. Stir for 1 minute so the pieces are coated with the oil and spices.

Add the rinsed red lentils to the pot. Stir for about 30 seconds to mix them evenly with the vegetables.

Pour the vegetable broth into the pot. Use a wooden spoon to scrape the bottom of the pot so nothing is sticking.

Raise the heat to high and bring the soup to a boil.

Lower the heat to medium-low so the soup bubbles gently. Cover the pot partway and cook for 10 minutes.

Add the drained chickpeas to the pot. Stir them into the soup.

Continue cooking, partly covered, for 10 to 12 minutes, until the lentils are very soft and the cauliflower breaks apart easily when pressed with a spoon.

Use a potato masher or the back of a sturdy spoon to mash some of the cauliflower, lentils, and chickpeas right in the pot. Stop when the soup looks thick and creamy but still has some whole chickpeas and a few larger cauliflower pieces.