Peel and dice the vegetables, shallots and garlic, set aside the leaves from the celery stalks. Grate the lemon peel, squeeze out the juice.
Bring the vegetable trimmings and peel to a boil with 500 ml of water, season with salt and simmer slowly for about 10 minutes. Then empty through a sieve and continue to use as vegetable soup for the stew.
Boil the spelt rice in the vegetable soup once, then simmer over low heat for 20-25 minutes, drain (reserving the soup) and set aside.
Heat sunflower oil in a wide pot, slowly sauté the vegetables in it with the thyme without letting them take color. Pour in the remaining vegetable soup and simmer over low heat until tender.
Mix cooked vegetables with the spelt rice and season with lemon juice, salt and pepper.
Serve the stew in deep plates and garnish with lemon zest and celery greens.