• Preheat the oven to 375°F.
• Heat the 1 tablespoon of vegetable oil in a 12" cast iron skillet on medium-high heat.
• Saute the spinach for about 3 minutes, sprinkling kosher salt about halfway through cooking. No need to stir that often, just stir occasionally.
• Remove the spinach from the skillet and set aside.
• Add the diced bell pepper. Cook for about 4 minutes, sprinkling about 1/2 teaspoon (or to taste) kosher salt about halfway through cooking.
• While the bell pepper is cooking, beat the eggs in a medium bowl until the yolks and whites are homogenous. Add the milk and whisk until fully incorporated. Add the parsley and black pepper.
• Lower the heat to medium. Add the onion and saute for another 4 minutes, again sprinkling about 1/2 teaspoon (or to taste) of kosher salt about halfway through cooking.
• Add the spinach back to the skillet. Mix briefly to incorporate with the peppers and onions.
• Add the egg mixture to the skillet and place skillet in oven. Cook for 25 minutes or until a toothpick stuck in the egg comes out clean. Let sit for 10 minutes before slicing and serving.

If Baking with Crust

• Omit the spinach. Use 8 eggs with 1/2 cup of milk. Add the mixture to the pie crust after it has finished blind baking. Bake for 25 minutes, but it may need longer time. Just keep checking it with a toothpick after the top of the eggs appears set.