Heat a large skillet over medium-high heat. Add olive oil and potatoes and cook for 15 minutes, stirring occasionally, until potatoes are cooked through and slightly crispy on the outside.
Add chopped onions and cook for 5 minutes, until translucent.
Remove chorizo from casing and add to skillet. Break up the chorizo using your spatula and cook for 5 minutes.
Add eggs and let them sit for about 30 seconds. Then, gently stir them until the eggs are just cooked through. Remove from heat.
Heat up the corn tortillas over medium-high heat on a large skillet, griddle or comal. Fill with chorizo, potato and egg mixture and top with cilantro and queso fresco.