In a Dutch oven over medium high heat, add the oil, onion, carrots and celery, and mushrooms, stir to soften and wait for the mushrooms to release their water. Then add the garlic and cook for one more minute.
Add the coriander and herbs, stir until fragrant. Then add the stock, greens, cauliflower, tomatoes, vinegar and lentils, stir well and bring to a simmer. Cook for 15 minutes.
Combine cornstarch and 1/4 cup water to make a slurry and add to the pot to thicken the gravy. Cook for 2-3 minutes.
Remove from the heat. If you're using a ceramic Dutch oven, scoop the potatoes over the top or transfer the mixture to a casserole dish and spread the potatoes over the top and bake at 350° for 15 minutes.