Preheat large dutch oven or heavy-bottomed pot over medium heat.
Add oil, then sprinkle in flour when oil is hot. (Test the oil by dropping a pinch of flour in the oil; if it simmers, it is hot enough.) Toast flour in the oil, stirring for a few minutes until it turns golden brown.
Add onion, garlic, bell pepper, celery and salt and stir. Saute on medium heat until onion is translucent, about 3 minutes.
Add diced tomatoes, stock, bay leaf, dulse, Creole seasoning and Old Bay seasoning. Stir well and bring the pot to a simmer.
Add mushrooms and continue to simmer for 20 minutes until they become tender.
Taste and adjust seasoning. Serve over rice with a squeeze of lemon juice and garnished with parsley.
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Notes
Recipe Pro Tips:
For various textures, use a variety of mushrooms. King oyster mushrooms can be sliced vertically for long, thin pieces, or they can be shredded for more of a flaky seafood-esque texture.