Add oil and butter to a Dutch oven, and stir in the flour.
Heat to medium, stirring often for 20 minutes until the flour begins to deepen to the color of peanut butter. Continue to stir so the roux doesn’t burn.
Add the bay leaf, onions, celery, and green bell pepper, stirring until the onion is tender. Slowly add in the garlic and chicken stock while stirring.
The mixture will start to thicken and come to a boil.
Add crushed tomatoes, cajun seasoning, salt, sausage, and oka to the Dutch oven. Mix well and bring to a boil. Once boiling, reduce the temperature, cover the pot, and allow it to simmer for 15 minutes.
Add the shrimp, simmering for 8-10 more minutes. Remove from the stove.
Top the Gumbo with chopped parsley.
Serve.