Season the chicken breasts evenly with 1 teaspoon salt and 1 teaspoon pepper and place them in a large resealable bag.
In the bag add 1/4 cup minced cilantro, 3 tablespoons olive oil, 3 tablespoons lime juice, and 1 tablespoon taco seasoning. Remove excess air and seal, then massage the marinade into the chicken until evenly coated.
Refrigerate and marinate the chicken for at least 30 minutes and up to 2 hours (do not add additional lime earlier than 2 hours before cooking to avoid toughening the meat).
Preheat your grill or grill pan to medium-high heat (about 350–400°F).
Grill the chicken breasts 6 minutes per side, or until an instant-read thermometer inserted into the thickest part reads 165°F.
Transfer the chicken to a cutting board and let rest 5 minutes, then slice into strips or dice.
Warm the tortillas on the grill or char them slightly over an open flame if using corn tortillas.
Assemble each tortilla with grilled chicken and top with pico de gallo, queso fresco or cotija, sour cream, avocado or guacamole, and extra cilantro and lime juice as desired.