Clean and dry mushrooms and cut into halves vertically. In a large bowl, whisk together all marinade ingredients, aside from the fresh parsley. Remove half the marinade and set aside in a small saucepan.

Add fresh parsley to remaining marinade and add mushroom halves, tossing to coat. Pour mushrooms and marinade into a large ziplock bag and marinate for about one hour, flipping the bag over two to three times during the process. If using wooden skewers, presoak in water for one hour as well.

Place diced onion into a large frying pan. Add oil and sauté until soft and golden, about 15 minutes. Add garlic and sauté another one to two minutes until fragrant. Add chopped spinach to the pan and stir for about a minute until slightly wilted. Add chicken soup mix, water, and pepper, mixing well to combine. Remove from heat.

Place potatoes into a pot and fill with water to cover. Add 1/2 tablespoon of salt and boil until soft. Drain and roughly mash potatoes in the pot, using a potato masher. Add spinach mixture and nutritional yeast and mix well until evenly distributed into the mashed potatoes. Allow to cool for about 30 minutes.

Combine panko crumbs with Italian seasoning and place on a shallow plate. Form the potato mixture into 10 croquettes, about three inches (seven and a half centimeters) in diameter, and coat on all sides with crumbs. (I used a food stacker to get perfect circles.) Place on a greased baking sheet and spray each croquette generously with cooking spray.

To prepare the mushrooms, spray a baking sheet with cooking spray. Thread four mushroom halves vertically onto a seven-inch (18-centimeter) skewer and place on the greased baking pan. Spray generously with additional cooking spray.

Preheat oven to 425 degrees Fahrenheit (220 degrees Celsius). Place baking pan with mushrooms on the upper rack of your oven and the croquettes on the lower rack. Bake for 20–25 minutes, flipping skewers over about halfway through.

Simmer the reserved marinade over low heat until it thickens slightly, about 10–15 minutes.

Place a croquette on a plate and position a mushroom skewer on or near it. Drizzle with warm balsamic reduction and sprinkle with additional fresh parsley for garnish.