Heat a large, heavy-bottomed pot over medium heat. Once heated, pour in the oil. Add the onions, carrots, and celery to the pot and stir. Add the lentils. The vegetables will begin to get soft and break down and the lentils will crisp up a little, about 5 minutes. Lower heat if vegetables and lentils begin to brown too much.
Add the paprika, thyme, and garlic to the pot and stir until fragrant, about 1 minute. Season everything with salt and pepper.
Add in the cabbage, and chickpeas to the pot and stir to coat in the spices and oil. Season everything again with salt and pepper. Add the plum tomatoes and stir it all together, breaking up tomatoes with spoon a little bit as you stir. Add the vegetable stock to the pot and stir.
Bring the soup to a boil. Once boiling, lower the heat to a simmer and cook uncovered until lentils are tender, stirring occasionally, for about 30-40 minutes. You want all the flavors to meld nicely and for the cabbage to be very tender.
Stir in the spinach and bring the soup back up to a low boil. Lower the heat. Stir in the tamari (if using). Add more salt and pepper if needed (and any hot pepper, if you like it spicy!). Serve the chickpea, lentil, and cabbage stew nice and hot!