Slice the steak thin.
In a large ziplock bag, combine the chicken, lime juice, lime zest, olive oil, cilantro, garlic, chipotle in adobo sauce, cumin, oregano, and salt.
Marinate in the refrigerator at least two hours to overnight.
Heat the griddle or skillet over high heat.
Add the onion along with the chicken and marinade.
Cook until chicken is done and marinade has reduced.
This will only take about 8 minutes depending if your cooking surface is hot.
Divide the steak, onions among the tortillas.
Top with avocado, cheese, and salsa.