Place the mushrooms, with their stems removed, in a medium bowl. Drizzle them with 2 tablespoons of the olive oil and the sherry or white wine. Toss to coat. Set aside.
Chop the mushrooms stems and set aside.
In a large saute pan, heat the remaining 2 tablespoons of olive oil over medium-high heat. Add the onion and cook for about 2 minutes. Add the chopped mushrooms stems and continue cooking for another 2 minutes. Add the crushed red pepper flakes and the garlic. Cook for just a minute. Add the spinach, sun-dried tomatoes and artichokes. Continue cooking until the spinach wilts. Add the panko, nutritional yeast, salt and pepper. Remove from heat.
Preheat your oven to 350 degrees.
Place the mushroom caps onto a baking sheet. Using a spoon or a cookie scoop, fill each mushroom generously.
Bake the mushrooms for 30 to 40 minutes, depending on your mushroom size and variety. Test for doneness before removing from the oven.
Serve immediately and garnish with some chopped parsley.
Notes
Keep in mind that mushroom varieties and sizes will affect cooking time. Cremini mushrooms will take longer to cook through, while white button mushrooms cook much more quickly. Test for doneness before removing from the oven.If you need these gluten free, be sure to use gluten free breadcrumbs in place of panko.