Preheat the oven to 375°F (190°C).
Season chicken with salt, pepper, garlic powder, and oregano.
Dip each piece in beaten egg, then coat with breadcrumbs.
Heat olive oil in a large skillet over medium heat. Sear chicken for 2-3 minutes per side until golden.
Remove chicken and sauté mushrooms in the same skillet until tender.
In a baking dish, layer marinara sauce, chicken, mushrooms, and cheeses.
Bake for 20-25 minutes until cheese is melted and bubbly.
Let rest for 5 minutes before serving. Garnish with basil if desired.