Preheat your oven to 375°F (190°C).
Heat olive oil in a skillet over medium-high heat. Sauté mushrooms, onion, and garlic until the mushrooms turn golden brown and any liquid they release evaporates. Stir in the thyme and season with salt and pepper to taste. Allow the mixture to cool slightly before proceeding.
In a mixing bowl, whisk the eggs and cream together until well combined.
Place the pie crust in a 9-inch pie dish and add the mushroom mixture to the bottom.
Top with the grated cheese.
Pour the egg and cream mixture over the filling in the pie dish.
Place the quiche in the oven and bake it for 30 to 35 minutes, or until it sets and the top turns golden brown.
Allow your quiche to cool for a few minutes before slicing and serving.
