Heat a large skillet over medium-high heat. Add the chorizo and cook for 8–10 minutes, breaking it into small pieces with a wooden spoon, until fully cooked and slightly crispy.
While the chorizo cooks, wrap the tortillas in a damp paper towel and microwave for 30 seconds. Alternatively, warm them individually in a dry skillet for about 30 seconds per side.
Place a spoonful of cooked chorizo on each warm tortilla and top with the diced onion.
Serve immediately.
Notes
If the chorizo is very fatty, you may want to drain some of the excess fat after cooking.Red onion can be used for a slightly milder, sweeter flavor.Refrigerate the leftover cooked chorizo in an airtight container for up to 5 days.