Preheat your grill to medium-high heat. If using a grill pan, heat it over medium-high heat on the stove.
In a small bowl, mix together the garlic powder, onion powder, smoked paprika, salt, and black pepper. Rub the spice mixture evenly over both sides of the chicken breasts.
Drizzle olive oil over the chicken breasts and rub it in to coat them evenly.
Place the chicken on the grill and cook for 6-7 minutes on each side, or until the internal temperature reaches 165°F. Remove from the grill and let rest for 5 minutes.
While the chicken is resting, prepare the chipotle mayo by mixing mayonnaise, chipotle sauce, and lime juice in a small bowl. Adjust the chipotle sauce to your preferred spice level.
Toast the sandwich buns on the grill for about 1-2 minutes until lightly golden.
Assemble the sandwiches by spreading a generous amount of chipotle mayo on the bottom half of each bun. Layer with lettuce, sliced tomato, grilled chicken, and avocado. Top with the other half of the bun.
Serve immediately and enjoy your delicious grilled chicken sandwiches!