Boil the sweet potato cubes in salty water until tender (about 15 minutes).
Drain well, transfer to a bowl, mash with a fork, add the olive oil, crushed garlic and a pinch of sea salt, and mix to obtain a chunky puree. Set aside.
Heat the oven at 175°C/347°F .
Heat the coconut oil in a pan and add the onion, celery and carrot. Cook for five minutes, stirring frequently.
Add the lentils, the bay leaf, thyme, tomato sauce, water and lemon juice, bring to boil, cover with a lid and simmer for 15 minutes, until the lentils are almost cooked and the liquid thickened.
Season with salt and pepper, remove the bay leaf and thyme, and transfer to a baking dish.
Spread the sweet potato mash on top, drizzle with olive oil and cook in the oven for 15 minutes.
Serve garnished with chopped parsley leaves.