Heat the olive oil in a large pot over medium heat. Add the diced onion and cook until it softens, about 5 minutes. Stir in the minced garlic and cook for 1 minute more.
Add the sweet potato cubes along with the cumin, cinnamon, smoked paprika, turmeric, salt, and black pepper. Stir to coat the vegetables with the spices and cook for 2 minutes.
Pour in the drained chickpeas, diced tomatoes, and vegetable broth. Bring the mixture to a boil, then reduce the heat and simmer uncovered for 20 minutes, or until the sweet potatoes are tender when pierced with a fork.
Stir in the spinach and cook just until it wilts, about 2 minutes. Remove the pot from the heat and stir in the lemon juice. Ladle the stew into bowls and top each serving with chopped cilantro.