Preheat oven to 375F
Place mushroom caps top down on baking sheet
Whisk together balsamic vinegar, 1/4 tsp each of salt and pepper and brush mushrooms with mixture
Bake in the oven for 10-15 minutes, until tender
In a large pan over medium heat, cook shallots and garlic until until just caramelized, about 5-7 minutes
Add rosemary and cook for an additional 1-2 minutes. Then stir in spinach and broth and cook until spinach begins to wilt.
In a large bowl, combine vegetable mixture, beans, parsley, oat flour, nutritional yeast and remaining salt and pepper
Stuff each mushroom with the mixture and sprinkle the tops with a little extra oat flour and nutritional yeast
Bake for an additional 10-15 minutes, until heated throughout and just beginning to brown on top
Serve and enjoy!