Cook chorizo in an oven-safe skillet until browned, breaking it apart. Add onion and jalapeño and cook until onions turn translucent. Drain excess fat. Reserve one-third of the mixture.
Cheese Layer
Spread queso Oaxaca evenly over the skillet mixture. Top with reserved chorizo. Heat at 400°F until cheese bubbles.
To Serve
Garnish with cilantro and serve hot with tortillas.