Preheat the oven to 180°C.
First make the tomato sauce. Cut the onion into wedges. Halve the tomatoes and cut the red pepper into chunks. Put them in a baking tray and tuck the garlic cloves between the veggies.
Season with salt and pepper, then drizzle with oil.
Bake in the oven for 25-30 minutes, until the vegetables are tender and lightly browned.
Take the tray out of the oven and let the vegetables cool, then remove their skins.
Put the flesh of the veggies in a liquidiser together with cooking juices. Whiz until you get a sauce.
You can chill or freeze this sauce for later use, or continue with the recipe immediately.
Tear the cauliflower into small florets.
Heat some oil in a heavy based saucepan and gently sauté the cauliflower for 5 minutes. Add the tomato purée and the spices. Stir for one minute, then add the tomato sauce and a small glass of water. Season to taste.
Bring to the boil and gently simmer for 15 minutes.
Add the lentils and spinach and cook for another 5 minutes.
Serve warm.