Drain the hearts of palm, add them to a pot with water, bring to a boil, then let it simmer for 3 minutes. Drain the water, resave the hearts of palm.
On a cast iron skillet, add the oil, when hot add the mushrooms. Add salt and let them brown. Repeat with the remainder of the mushrooms until you have browned them all. Reserve.
In the same skillet, add more oil, then add the mirepoix. Sauté until golden. Then add the tomato puree, stir for 1 minute, deglaze the pan with the wine, stir for 1 minute, then add the vegan cream, salt, pepper and garlic powder, the mustard, and the mushrooms, add some water if needed, let it simmer in low heat for 10 minutes.
Add the pickles and the pickle brine, the hearts of palm, let it simmer for 2 minutes, if your strogonoff is a bit too acidic, add some tomato ketchup or a tiny bit of brown sugar.
Turn off the heat and serve it with a side of stir potatoes and rice.