In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add the chopped onion and sauté until soft and translucent, about 3-4 minutes.
Add the minced garlic to the skillet and cook for another minute until fragrant.
Incorporate the sliced mushrooms into the skillet and cook until they are browned and have released their moisture, about 5-7 minutes.
Add the chopped spinach and thyme to the skillet, and continue cooking until the spinach is wilted. Season with salt and pepper to taste. Remove from heat and set aside to cool slightly.
In a mixing bowl, whisk together the eggs and heavy cream until well combined. Season with additional salt and pepper if desired.
Add the sautéed spinach and mushroom mixture into the egg mixture, stirring until everything is well incorporated.
Place the pre-made pie crust into a quiche or pie dish. Pour the filling into the crust, making sure the veggies are evenly distributed.
Sprinkle the shredded cheese on top of the filling.
Bake in the preheated oven for 35-40 minutes, or until the quiche is set in the middle and lightly golden on top.
Allow the quiche to cool for 10 minutes before slicing and serving.
Notes
Garnish each slice with fresh herbs for added flavor.