Preheat oven to 350 F degrees. Line a baking sheet with parchment paper and set aside.
Heat butter and oil in a pan on medium heat. Once hot, add chopped garlic. Saute for 30 seconds.
Add chopped onions. Saute for 1-2 minutes.
Add sliced mushrooms. Also add salt and pepper and cook for around 5 minutes, till mushrooms are soft and done.
Add few sprigs of thyme and cook for another minute. Remove from heat and set aside.
Cut the baguette into diagonal slices, around 1/2 inch each. Arrange them on a baking sheet and put them in the oven at 350 F degrees for around 6 minutes. You can also toast the bread on pan.
While the bread slices are getting toasted, mash the avocados in a bowl.
Add salt, pepper, garlic and salt and lime juice and mix till everything is well combined.
Take out the toasted slices out of the oven and top them with the mashed avocado.
Top the avocado with the prepared mushroom mixture.
Garnish with fresh thyme and sprinkle some crumbled feta cheese on top. Serve immediately!