Preheat the oven to 350 degrees Fahrenheit. Prepare an 8-inch square baking dish by either buttering it or spraying it with a non-stick baking spray.

In a large skillet, cook the diced bacon over medium heat until the fat is rendered and the bacon is crisp. Once cooked, transfer the bacon to paper towels to drain. Reserve approximately 1 teaspoon of bacon grease in the skillet.

Utilize the remaining bacon grease in the skillet to cook the chopped onion. Maintain a medium heat and stir until the onion is tender.

Introduce the fresh spinach leaves to the skillet. Continue to stir constantly, cooking until the spinach is wilted and any excess moisture has evaporated.

Transfer the cooked spinach and onion mixture to the prepared baking dish. Evenly distribute the cooked bacon over the spinach, followed by an even layer of the shredded cheese.

In a separate mixing bowl, whisk together the low-fat milk and all-purpose flour until the mixture is smooth.

Continue to whisk, adding in the eggs and egg white. Once incorporated, add the ground black pepper, salt, onion powder, and dried oregano. Mix until all ingredients are well combined.

Pour this egg mixture evenly over the spinach, bacon, and cheese layers in the baking dish. If desired, lightly sprinkle the top with sweet paprika for added flavor and color.

Place the baking dish in the preheated oven. Bake for 30 to 40 minutes, or until the quiche is set and firm.