Heat oil in a large pot and add onions, celery, and red peppers along with a pinch of salt and red pepper flakes if you desire. Sauté veggies until the onions have softened and become translucent.
Add in minced garlic and ginger and sauté until fragrant.
Stir in spices and herbs, and sauté for an additional minute.
Add the sweet potato and cauliflower, stir well to coat the spices.
Pour in the lentils, vegetable broth and water, and give everything a big stir. Taste the broth at this stage and season with an additional pinch of salt if needed. Allow the soup to come to a boil, then reduce to a rolling simmer and cook uncovered for about 13 minutes.
At the end, remove the pot from the heat and throw in the spinach, stirring the soup until it wilts. Finally, add the lemon juice and adjust salt and pepper to taste before serving. Enjoy!