Heat a large pot over medium heat. Add the diced onion and carrots. Cook until the onion softens, about 5 minutes.
Stir in the minced garlic along with the cumin, coriander, cinnamon, and turmeric. Cook for 1 minute until the spices smell fragrant.
Add the rinsed lentils, diced tomatoes with their juices, and vegetable broth. Bring the mixture to a boil.
Reduce the heat to low and simmer uncovered for 25 to 30 minutes, or until the lentils are tender.
Stir in the lemon juice. Taste and season with salt and black pepper as needed.
Ladle into bowls and top each serving with the chopped cilantro.