Wash the cauliflower and chop the head into small florets (or take them apart with your fingers). Peel and dice the onion and the sweet potato.
Heat a pot or cocotte with olive oil. When hot, sauté the onion until translucent (see post above for step-by-step pictures).
Add the cauliflower and the sweet potato and sauté for 10 minutes over medium-high heat.
Add the lentils, coconut milk, diced tomatoes and water. Cover with a lid and simmer for 20 minutes over medium heat.
Add the garam masala and a pinch of salt.