Over medium heat, melt the olive oil or butter in a nonstick skillet for 1 minute, until warm.
Crumble the feta into the pan. Once the cheese melts and begins to brown, crack the eggs over the feta (at this point, you can add pesto or chili crisp for a different flavored fried egg). Sprinkle over a pinch of salt and pepper, then immediately cover the eggs and reduce the heat to low.
Cook the eggs until the whites are opaque and the yolks are cooked to your liking. In the meantime, heat the tortillas and prepare any toppings.
Once the eggs are done, use a spatula to transfer them to a tortilla or a slice of toast, then add any toppings. Serve immediately.