Optional toppings and side dishes: guacamole, sour cream, salsa, fresh cilantro, rice, or beans.
Cut large chicken breasts in half width-wise and pound until an even thickness. Place in a large ziplock bag. Whisk together marinade ingredients (lime juice, lime zest, olive oil, oregano, garlic salt, cumin, crushed red pepper, and black pepper). Pour marinade over chicken, zip bag, and refrigerate for 2 to 4 hours (not longer than 5 hours). Cut whole onion into strips, leaving the root intact. Core peppers, remove seeds, and cut in half lengthwise.
Generously oil the grill grates and preheat grill to medium. Place the onions and peppers on the grill and cook until tender-crisp, about 7 minutes for the peppers and 12 minutes for the onion, flipping halfway through. Simultaneously cook the chicken breast 7 to 8 minutes per side or until cooked through and chicken reaches 165 F. Set chicken aside to rest for a few minutes so the juices can redistribute. The grill can be turned off, using the residual heat to warm the tortillas wrapped in foil. Thinly slice the breasts and peppers and cut the root off the onion. Display on a platter for everyone to serve themselves.
Per serving: 749 calories, 25 grams fat (6 grams saturated fat), 101 milligrams cholesterol, 1,302 milligrams sodium, 85 grams total carbohydrates, 6 grams fiber, 46 grams protein.
