Preheat oven to 400f.
Spray non stick in a large nonstick skillet over medium-high heat. Add in your chopped mushrooms in 3 batches. You want them to cook until they have lost their moisture and are nice and brown. Mushrooms release alot of water during cooking so it's important to get that water out otherwise the texture of the mushrooms will be soggy.
Once you've cooked all your mushrooms, add your garlic to the skillet and cook for 1 minute.
Add all your mushrooms back to the skillet.
Add your cream cheese, salt and onion powder in and mix until melted about 2 minutes.
Add in your parmesan, gruyere and milk and mix well. Stir until bubbly about 2-3 minutes.
While that's cooking, mix your melted butter and breadcrumbs together.
Once your mixture is done cooking, pour it into a shallow baking dish. I used an 8 inch ceramic dish. Spread it evenly. Top with breadcrumb mixture.
Bake for 15-20 minutes until your breadcrumb mixture is golden brown.
Serve immediately with toasted baguette.