Dice the onion, green pepper, and celery, and mince the garlic so the trinity is ready before the roux starts. Slice the mushrooms and cut the vegan kielbasa into rounds about a half inch thick.

Heat a dry skillet over medium-high heat and add the okra in a single layer. Cook it for 5 to 6 minutes, turning once, until the slices are browned at the edges and the sticky surface has dried out. Move the okra to a plate and set it aside. This step keeps the stew from turning ropey later.

Warm the olive oil in a heavy Dutch oven over medium heat, then whisk in the flour until the mixture is smooth. Cook it, whisking almost constantly, for 25 to 35 minutes, until the roux turns the color of dark chocolate. Keep the heat at medium and pull the pot off the burner for a few seconds if it ever smells scorched.

Add the onion, pepper, and celery to the roux and cook for 6 to 8 minutes, until they soften and start to glaze. Stir in the garlic and mushrooms and cook for another 5 minutes, until the mushrooms give up their liquid and it cooks off.

Stir in the tomato paste, Cajun seasoning, smoked paprika, thyme, and oregano and cook for 1 minute, until the spices smell toasted. Pour in the diced tomatoes and vegetable broth and stir well to work the roux into the liquid. Add the kidney beans, sliced kielbasa, tamari, hot sauce if you're using it, and the bay leaves.

Bring the pot to a gentle boil, then lower the heat and simmer, partly covered, for 30 minutes, stirring now and then so nothing sticks. Add the seared okra and simmer for 10 more minutes, until the okra is tender and the broth has thickened enough to coat a spoon.

Take the pot off the heat and lift out the bay leaves. Stir in the gumbo file powder and the lemon juice, then taste and adjust the salt and pepper. Ladle the gumbo over bowls of white rice and top with green onions and parsley.