Saute onion in olive oil for 1-2 minutes. Add garlic and continue to saute for another minute.
Add the celery, mushrooms and carrots and saute another couple of minutes.
Mix in the broth and lentils to the pot. Bring to a boil then turn down heat and simmer for about 20 minutes.
Stir in the kale, zucchini, brown rice (See Note) and spices. Simmer an additional 10 minutes. Check the lentils to make sure they are tender.
Note: I added the brown rice fully cooked to minimize the cooking time of the soup. However, you could add 1/3 cup brown rice with the lentils and add 1 additional cup of broth. Your soup might need to simmer an extra 5-10 minutes.