In a large skillet over medium heat, cook the bacon to desired crispness. Place the cooked bacon on paper towels to drain excess grease. Remove all but approximately 1 tablespoon of bacon grease from the skillet and lower the heat to medium-low.
In a medium-size mixing bowl whisk together eggs, salt, black pepper, and green chiles.
Add egg mixture to the skillet. Scramble the eggs until they are no longer runny, stirring often. Add in bacon and spinach and cook for approximately 1-2 minutes until the spinach has wilted.
Remove egg, bacon, and spinach mixture and wipe frying pan clean.
Place one tortilla in the skillet (or cast iron griddle) and cook one side for approximately 15 seconds and set aside. Repeat with a second tortilla and flip over to crisp the second side while adding the filling.
Cover the tortilla with ¼ cup of cheese and ¼ of the egg mixture leaving an approximately ½ inch border around the tortilla. Top egg mixture with another ¼ cup of cheese and cover with the second tortilla, cooked side down.
Cook for approximately 60-90 seconds letting the bottom layer of cheese melt and the tortilla get crispy.
With a spatula lightly press down on the quesadilla before carefully flipping it over. Cook for an additional 60-90 seconds.
Remove from the frying pan and place on a cutting board. Allow quesadilla to cool for 1-2 minutes before cutting with a pizza cutter or sharp knife.
Repeat for remaining quesadillas.
Serve quesadillas warm with fresh salsa or avocado slices.