In a large stock pot or dutch oven, warm the olive oil over medium heat. Add the onions and saute for 8-10 minutes. Then add the garlic and saute for another 2-3 minutes.
Add in the diced carrots and celery. Saute for 5-7 minutes or until slightly softened.
Add the cumin and curry powder. Stir through the vegetables until warmed, about 30 seconds.
Add the tomatoes and their juices, the lentils, the broth, and the red pepper flakes, if using. Bring to a boil, then simmer for 25-30 minutes, or until the lentils are soft and tender. Add additional water while simmering, if needed.
While the soup is simmering, lightly pan-fry the sausage links or the tempeh. Add to the soup to cook through completely.
Serve warm, topped with chopped parsley.