Prepare the mushrooms by wiping off the caps and removing all of the stems.
Make the filling by mixing the cream cheese, spinach, artichoke hearts, sour cream, Parmesan cheese, red pepper flakes, garlic powder, and salt together in a small bowl. Adjust flavor to taste as desired.
Line the mushrooms up in a baking dish, cap side down. Scoop approximately 1 Tablespoon of the spinach artichoke dip into each mushroom (more or less depending on size of mushroom and the hole). Make a mound of the mixture above the hole as it will not all fit inside.
Repeat with all of the mushroom caps. Drizzle with a little olive oil and sprinkle the tops with additional Parmesan cheese if desired. (The extra Parmesan is great for getting a little crispy cheese crust on top).
Bake the mushrooms for 10-15 minutes until the mushrooms are tender. Bake longer if you want softer mushrooms, however they will become more difficult to eat by hand. Serve immediately.
Crimini mushrooms are also called baby portabellos. You could use any size or type of mushroom you would like.To ensure a truly vegetarian dish, make sure you use vegetarian cheeses.