Soak lentil in plenty of cold water and leave overnight. Strain and rinse then cover with cold water and bring to boil. Pour out the water and pour in new hot water. Repeat this operation then cook until tender.
Simmer finely chopped onion in a casserole with olive oil over a low heat until tender and aromatic. Add very finely chopped carrot and simmer over a low heat until tender and aromatic. Put in finely chopped peas, potato, courgette, separated flowers of cauliflower and tomato concentrate. Mix, simmer for a while and cover with water to cook for about 15 minutes. After that add lentil (without its cooking water) and simmer all together briefly.
In case baby is 6-9 months old, pass a portion of the dish through a strainer to get a dense puree adding some broth or olive oil (the puree is almost sweet from onion and carrot), if a child is older season with salt and serve to your taste and habit.