Preheat oven to 350 degrees.
Take a moist paper towel and wipe off any dirt on mushrooms. Gently scoop out stems (if any) and insides of mushrooms to make room for stuffing. Reserve the stems and insides.
In a large sauté pan over medium heat, drizzle some olive oil. Add diced onions and sauté until they turn translucent. About 5 minutes.
Add your reserved insides of mushrooms to pan. Cook for another 3 minutes.
Add salt, pepper, garlic powder, onion powder, oregano and spinach to pan. Cook for 2-3 minutes until spinach has wilted.
Add your sour cream, cheese and bread crumbs to pan. Turn heat down to low, and mix everything around until it turns into a moist stuffing like consistency.
Take pan off heat. Set aside to cool a bit.
On a baking sheet sprayed with non stick spray, add your hollowed out mushroom caps. Take a spoon and fill mushrooms with stuffing.
Bake in preheated oven for 15-18 minutes.
Enjoy!