Heat the olive oil in a large pot over medium heat. Add the chopped onion and cook until it softens.
Stir in the minced garlic and diced carrots. Cook for another two minutes until the garlic smells fragrant.
Add the cumin and harissa paste. Stir to coat the vegetables evenly.
Pour in the diced tomatoes with their juices and the vegetable broth. Bring the mixture to a simmer.
Add the rinsed lentils and season with salt and black pepper. Reduce heat to low, cover, and cook for 25 minutes until the lentils are tender.
Taste and adjust salt if needed. Remove from heat and let the stew sit for five minutes before serving.
Ladle into bowls and top with chopped parsley. Serve with lemon wedges on the side.