In a medium bowl, combine olive oil, lime juice, garlic powder, cumin, salt, and pepper to create a flavorful marinade. Add the boneless, skinless chicken breasts, ensuring they are well coated. Let the chicken marinate for at least 20 minutes at room temperature.

Preheat your grill or grill pan over medium-high heat for about 5 minutes. Once hot, add the marinated chicken breasts to the grill, cooking for 6-7 minutes on each side, or until the internal temperature reaches 165°F (75°C).

While the chicken is grilling, slice the bolillo or telera rolls in half and place them cut side-up on a baking sheet. Toast them under the broiler for 2-3 minutes if desired.

Once the chicken has cooked through, remove it from the grill and let it rest for a few minutes before slicing it into strips. Layer the sliced chicken on the bottom half of each roll along with shredded lettuce, fresh tomato slices, and creamy avocado.

Top the chicken and veggies with pickled jalapeños and a dollop of sour cream or crema before placing the top half of the roll over the fillings, pressing gently to keep everything together.

Slice the sandwiches in half if desired, and serve immediately.