First, use a vegetable chopper to dice the white onion, mushrooms, and red bell pepper. Chop the sausage links into ½” slices.
Heat a skillet to medium heat and coat with cooking spray. Once warm, add the bell pepper, onion, and sausage into the skillet. Cook until the peppers are translucent and sausage is fully cooked (if not using pre-cooked). Add the mushrooms into the mixture half way through.
Prep the spinach. If using frozen spinach which means it’s CRUCIAL that you remove excess water. Allow the frozen spinach to thaw or heat it up in the microwave for 30 seconds. Wrap your spinach in paper towel, and over the sink or a bowl use your hands to generously squeeze the water out similar to ringing out a sponge.
Preheat the oven to 350°F.
Add the drained spinach to the skillet and use a rubber spatula to break it apart. Add in the pepper jack cheese. Stir all together until the spinach is broken down, the cheese is gooey, and all of the veggies are soft and well cooked.
Crack the eggs into a mixing bowl and add egg whites, too. Whisk together until the yolks are broken down, and add in the milk. Whisk again. Stir in green goddess seasoning.
Then, spray a pie dish with cooking spray. Add in all of the vegetables, sausage, and cheese from the skillet to the pie dish. Add the egg mixture over the veggies and then sprinkle all of the feta cheese on top. Stir slightly so it’s combined.
Bake for 35-40 minutes or until the center of the quiche is completely firm. Stick with a toothpick to check for doneness as you would a cake or brownies.
Top with fresh avocado, tomatoes, more feta crumbles, etc. Slice and enjoy!