Begin by baking your 9-inch unbaked pie shell according to the package instructions until it's lightly golden, about 10-15 minutes. Allow the crust to cool fully on a wire rack.

While the crust cools, preheat your oven to 350°F (175°C).

Sauté the four slices of thick-cut bacon in a skillet over medium heat until crispy, about 5-7 minutes. Drain on paper towels and chop into bite-sized pieces.

In the cooled pie crust, sprinkle the feta cheese crumbles evenly across the bottom. Next, layer on the deseeded and drained tomatoes, chopped spinach, green onions, and the crispy bacon pieces.

In a mixing bowl, whisk together the four room temperature eggs with ⅓ cup of cream, ¼ teaspoon of salt, ⅛ teaspoon of black pepper, ⅛ teaspoon of ground mustard, and a pinch of red pepper flakes until fluffy and well combined.

Carefully pour the egg mixture over the layered ingredients in the pie crust. Ensure even distribution to bind everything.

Place the assembled quiche in the preheated oven and bake for 40-45 minutes until the top is golden brown and a knife inserted in the center comes out clean.

Once baked, remove the quiche and let it rest for 5-10 minutes to set.