Preheat oven to 350 degrees F.
Bring a large dutch oven to medium heat and melt the butter. Add mushrooms and a pinch of salt and cook until all sides are golden brown, occasionally stirring gently, about 10 minutes.
If using vegan sausage, add and sauté until golden-brown, occasionally stirring, about 5 minutes.
Add onions, bell peppers, celery and garlic and cook until tender, stirring occasionally, about 5 minutes.
Add onion powder, garlic powder, nutritional yeast, sweet paprika, cayenne, cumin, dried sage, dried oregano, dried parsley, and black pepper. Stir occasionally and cook for 5 minutes to toast the spices.
Add chopped tomatoes, tomato paste, vegan Worcestershire sauce, rice or cider vinegar, tamari or soy sauce, liquid smoke, fire roasted tomatoes, vegetable stock, fresh thyme, and bay leaves. Stir together and bring to a simmer. (You can leave the thyme sprigs and bay leaves whole as you will remove them at the end.)
Once at a simmer, stir in the rice and the peas (if using), mix well, and cover. Place in center of oven and bake for 30 minutes. Take out of the oven and give it a taste. If the rice needs to cook longer or seems dry, drizzle some more vegetable stock on top and pop it back in the oven for a few more minutes.
Once done, season with salt and pepper to taste. Remove the bay leaves and thyme sprigs and serve in bowls. Sprinkle with desired garnishes.