To prepare tacos: Position oven racks in top third and lower third; preheat to 450°F. Liberally coat 2 large baking sheets with cooking spray. Stir together chicken, sour cream, taco seasoning and salt in a medium bowl until well combined.
Wrap tortillas in damp paper towels; microwave on High until warm and pliable, 30 to 45 seconds. Carefully place 4 tortillas on each baking sheet. Spread chicken mixture evenly over 1 half of each tortilla; top with cheese. Fold the tortillas in half and gently press, ensuring tortillas stay folded.
Bake, flipping the tacos and rotating the baking sheets between top and bottom racks halfway through, until the tortillas are golden and crisp, 14 to 16 minutes.
Meanwhile, prepare crema: Place avocado in a medium bowl; use a fork to mash until smooth. Add sour cream, cilantro, lime juice, oil, garlic and salt; stir until combined and mostly smooth. Cover and refrigerate until ready to use.
Serve the tacos with the crema, and with lime wedges and/or pico de gallo, if desired. Additional reporting by Carrie Myers, M.S. and Linda Frahm