Simmer until lentils and vegetables are fully tender, about 5 minutes.
The mushrooms in step 2 make it possible to saute the vegetables without oil. They release a lot of water. When they stop releasing water and the liquid dries up, it is a good time to move on the next step.
Fresh tomatoes also work in this recipe. Use 200 g fresh tomatoes (deseeded) with 200 g passata.