Heat your large pot over medium heat and add a tablespoon of oil. Once shimmering, add the diced onion and cook, stirring frequently, until it turns translucent and starts to caramelize, about 8 minutes. The onions should smell sweet and look golden.
Add the minced garlic to the pot and cook for another minute, stirring constantly until fragrant—your kitchen will fill with a warm aroma of garlic and spices.
Stir in the toasted cumin, cinnamon, and smoked paprika, cooking for 30 seconds to release their fragrant oils. Be careful to stir constantly so they don't burn—they should become aromatic and slightly darker.
Add the sliced carrots and stir well, allowing them to coat with the spices. Cook for about 5 minutes, stirring occasionally, until they start to soften and turn a little golden on the edges.
Pour in the crushed diced tomatoes, stirring to combine everything and scraping up any flavorful bits stuck to the bottom of the pot. Let this simmer gently for 5 minutes until the mixture thickens slightly and smells rich.
Drain and rinse the chickpeas, then add them to the pot along with the vegetable broth. Stir everything together and bring to a gentle simmer. Cover the pot loosely and lower the heat to maintain a low simmer, cooking for about 20 minutes to let the flavors meld and the chickpeas to absorb the spices.
After simmering, stir in the sliced zucchini and cook uncovered for another 10 minutes, or until the zucchini is tender but not mushy, and the sauce has thickened to your liking. You should see the vegetables softening and the sauce becoming fragrant and slightly glossy.
Season the stew with salt and pepper to taste. Finish with a squeeze of fresh lemon juice to brighten the flavors. Give everything a gentle stir to distribute the seasoning evenly.
Remove from heat and let the stew sit uncovered for 5 minutes. This resting time allows the flavors to deepen and the sauce to thicken just a bit more, creating a luscious, hearty dish.
Scoop the chickpea vegetable tagine into bowls, garnish with fresh herbs if desired, and serve hot. Enjoy the warm, aromatic comfort of this simple but richly flavored stew.