Sauté mushrooms and 1 tablespoon of vegan butter in a pan for approximately 5 to 6 minutes. Remove from the pan and set aside in a bowl with a lid or a plate on top to keep them warm. Add 1 teaspoon of vegan butter to the same pan as well as the chopped chard, minced garlic, and nutmeg. Cook for 2 to 3 minutes until the chard is wilted, fragrant, and soft, but still bright in color.
In a small sauce pan, whisk together maple tahini dressing, smoked gouda, and water over medium-low heat until melted and smooth.
Assemble with some cheese sauce on the bottom of the bun, then add the sautéed chard, the veggie burger patty, the sautéed mushrooms, more cheese sauce on top and then the top bun.