Heat the olive oil in a large pot over medium heat. Add the onion and garlic and cook, stirring occasionally, until the onion is tender, about 5 minutes.
Add the vegetable broth, lentils, cumin, oregano, black pepper, red pepper flakes, and salt. Bring to a boil, then reduce the heat and simmer for 20 minutes, stirring occasionally.
Add the spinach, parsley, and lemon juice and cook for 5 minutes, stirring occasionally.
Serve the soup hot.
Interesting Facts
Lentils are an excellent source of plant-based protein.
Spinach is an excellent source of vitamins A and K, and iron.