Heat the olive oil in a large saucepan or Dutch oven over medium-low heat. Add the leek and cook for 5–6 minutes, until softened.
Add the garlic, cumin, coriander, turmeric and chilli flakes, if using.
Cook for about 1 minute, until fragrant. Add the chickpeas and stock.
Bring to a gentle simmer and cook for 10 minutes.
Using the back of a wooden spoon or potato masher, roughly crush some of the chickpeas directly in the saucepan. Aim to crush about ¼ of them, leaving plenty whole.
Add the zucchini and simmer for 5 minutes, then add the peas and approximately two-thirds of the roasted cauliflower. Cook for another 2–3 minutes.
If the stew has become thicker than you’d like, add a splash of extra stock.
Place the tahini in a small bowl and gradually whisk in about 80ml hot broth from the stew until smooth.
Stir the tahini mixture back into the saucepan. Add the spinach and stir until just wilted.
Remove from the heat. Stir through the lemon zest, 1 tablespoon lemon juice, ½ teaspoon honey and parsley.
Season generously with salt and black pepper. Taste and adjust with additional honey, lemon or salt as needed.
Divide between bowls and top with the reserved roasted cauliflower, parsley, black pepper and a drizzle of olive oil.