Liberally season both sides of each chicken breast with plenty of salt and pepper. In small bowl, combine chipotle chili powder, cumin, and garlic powder, then sprinkle spice mixture evenly over both sides of each chicken breast.
Heat large non-stick skillet over medium-high heat. Once skillet is very hot, add chicken. Cook 3 to 5 minutes without disturbing chicken, until chicken is nicely browned (or blackened, if you prefer) on one side.
Flip chicken over, cover skillet with lid, and reduce heat to medium. Cook approximately 5 to 7 minutes more, depending on thickness of chicken breasts, until chicken is completely cooked through. Transfer cooked chicken to cutting board and let rest 5 minutes. After 5 minutes, cut chicken breasts into bite-sized pieces.
Heat frozen cauliflower rice following instructions on package. If using fresh cauliflower rice, place in large skillet with 1 tablespoon water. Cover skillet with lid and cook over medium heat until cauliflower rice is fully cooked through.
Drain liquid from cauliflower rice (fresh or frozen), then toss cauliflower rice with juice of half of one lime (approximately 1 tablespoon) and ¼ teaspoon salt.
In small bowl, stir together mashed avocado, juice of other half of lime (approximately 1 tablespoon), and ¼ teaspoon salt.
Split cauliflower rice evenly into 4 serving bowls. Top rice with chicken, shredded lettuce, guacamole, and pico de gallo (optional). Garnish with additional lime wedges, if desired, and serve burrito bowls warm.