Dice the zucchini, red bell pepper, and yellow onion into bite-sized pieces; mince the garlic and cut the seitan into small cubes.
Heat the olive oil in a large pot or tagine over medium heat, then add the onion and cook for 3-4 minutes until translucent.
Stir in the garlic, cumin, coriander, cinnamon, and turmeric, toasting the spices for 1 minute until they become fragrant.
Add the seitan cubes and brown them slightly for 3 minutes, then stir in the chickpeas, red lentils, zucchini, and bell pepper.
Pour in the tomato puree and vegetable broth, stirring well to combine all ingredients.
Bring the mixture to a gentle simmer, cover, and cook for 20-25 minutes until the lentils are soft and the vegetables are tender.
Stir in the nutritional yeast, sea salt, and black pepper, then fold in the fresh spinach until it just begins to wilt.
Finish with a squeeze of fresh lemon juice before serving to brighten the deep, earthy flavors.