Preheat the oven to 350°F/180°C.
In a small saucepan, heat the oil over medium-high heat.
Add the chopped onion and cook, stirring for 5 minutes or until the onion is translucent.
Line a pan with the tortillas and sprinkle with the sauteed onion.
Gently break eggs into a cup, keeping yolks intact, then pour over the tortillas.
Sprinkle with mozzarella cheese.
Bake to the desired doneness (time can change depending on your oven) *check my tip and tricks below.
Remove from the oven, sprinkle with salt and pepper, and enjoy immediately.