In a heavy skillet, cook the bacon over medium heat until crisp. Remove with a slotted spoon and drain on a paper towel. Set aside.

Preheat oven to 425 F. Grease a 11-12" oven-safe skillet or pie plate and set aside.

In the pan drippings, sauté the spinach until almost wilted. Add the minced garlic and cook 30-60 seconds longer over medium-low heat until fragrant. Remove from heat and add the vinegar mixture. Stir until combined.

While the bacon is cooking, combine the apple cider vinegar and mustard in a small bowl and set aside. Crack the eggs into the jar of a blender and add the salt, pepper, onion powder, and heavy cream. Pulse until combined and set aside.

When the spinach is done cooking, transfer to the prepared pan. Sprinkle with the drained bacon, making sure the ingredients are evenly distributed. Sprinkle evenly with both cheeses and then the chopped green onions. Pour the egg mixture over the bacon and spinach mixture. Bake for 25-30 minutes or until puffed and lightly golden on top and it doesn't jiggle in the center when shaken. Remove from the oven and allow it to cool 10-15 minutes before cutting into wedges.