Add the butter to a skillet and heat over medium. When the skillet is hot, add the egg and fry until over-easy (or your preferred level of doneness).
While the egg cooks, spread the chili garlic paste on one half of the tortilla. Add the shredded cheese on top of the chili garlic sauce.
When the egg is finished cooking, place it on top of the shredded cheese on the tortilla. Top with the fresh spinach, then fold the tortilla closed.
Transfer the stuffed and folded tortilla back to the skillet used to cook the egg. Continue to cook over medium on both sides until golden brown and crispy and the cheese is melted on the inside.
Slice the breakfast quesadilla in half, then enjoy!