Preheat the oven to 350°F and grease a 9x13-inch casserole dish with cooking spray.
Add avocado oil to a frying pan over medium heat. Add sliced mushrooms to the pan and cook over medium heat, tossing frequently for about 5 minutes. Add salt, pepper, and dried thyme to the pan, mix into mushrooms and cook for an additional minute. Remove the pan from the heat and allow the cooked mushrooms to cool.
Crack eggs directly into the casserole dish and whisk them together. Add the soup to the casserole dish and mix together with the eggs. Pour cooked mushrooms and crumbled feta into the casserole dish and mix in with a spoon.
Place the casserole dish in the oven and bake for 45 minutes at 350°F. Remove the casserole from the oven, allow to cool slightly and then slice into 12 even squares.
This nutritional information refers to each serving of the entire recipe and not just the products used as ingredients.