Heat oil in a large skillet, add onions and cook, stirring, until translucent, about 2 minutes.
Add the nopales and let them sweat and darken for about 5 minutes, stirring once or twice. They may exude a gelatinous liquid that will begin to dry out.
Add red chile sauce and stir for another 2 minutes.
Meanwhile, in a medium bowl whisk eggs and then add them to skillet and cook for 2 to 3 minutes or until eggs are cooked thoroughly.
Notes
Serve with warm red chile sauce and corn tortillas.