Preheat oven to 375 degrees.
Thinly slice your onion and then cut those slices in half. Next, slice and chop about 16 ounces of mushrooms.
Heat up about 1 tablespoon of olive oil in a large skillet over medium heat. Add your sliced onion and saute for about 5 minutes or so. Stir frequently to keep them browning evenly. Add about 1/2 tablespoon of water and stir again.
Next, add your chopped mushrooms and cook for about 6 minutes. Add 1 teaspoon of fresh thyme, 2 cloves of minced garlic and 1/2 teaspoon of salt. Stir everything and continue frying until the onions and mushrooms are nice and caramelized.
In a small bowl, add 1 teaspoon thyme, 1 clove minced garlic, 1/2 teaspoon salt, 1/2 cup panko bread crumbs, 1/3 cup parmesan cheese and 2 tablespoons butter, softened. Stir well until everything is combined and it's nice and crumbly.
Take about 1-2 tablespoons of this parmesan mixture and mix it into the mushrooms and onions. Spread the fried mushrooms and onions in a small pan. Cut 2 ounces of cream cheese into small pieces and scatter over the top of the mushroom mixture.
Spread the remaining parmesan and panko crumb mixture all over the top.
Bake for about 20 minutes or until the top is golden brown.