Drain and press the extra firm tofu to remove excess moisture, then cut into small 1/2-inch cubes.
Rinse the red lentils thoroughly under cold water until the water runs clear to ensure a clean flavor.
Chop the zucchini into half-moons and break the cauliflower into bite-sized florets.
Place the tofu cubes, rinsed lentils, cauliflower, zucchini, turmeric, garlic powder, and onion powder into the slow cooker.
Pour the vegetable broth over the ingredients and stir gently to combine the spices.
Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours until the lentils are soft and the stew has thickened.
Stir in the nutritional yeast, hemp hearts, and fresh spinach, allowing the heat of the stew to wilt the greens for 2 to 3 minutes.
Finish by stirring in the lemon juice and seasoning with sea salt and black pepper before serving hot.