In a mixing bowl, combine the shredded chicken, ranch dressing, chipotle sauce, salt, and pepper. Stir until the chicken is evenly coated.
Lay a large flour tortilla flat on a clean surface. Place about ¼ of the chicken mixture in the center of the tortilla.
Top the chicken with shredded lettuce, diced tomatoes, shredded cheese, and avocado slices if desired.
Fold in the sides of the tortilla, then roll it up tightly from the bottom to the top, sealing the filling inside. Repeat with the remaining tortillas and filling.
Heat a large skillet or grill pan over medium heat and add a small amount of olive oil.
Place the burritos seam-side down in the skillet. Grill for 3-4 minutes on each side, or until the tortillas are golden brown and crispy, and the cheese has melted inside.
Remove the burritos from the skillet and let them sit for a minute before slicing them in half.
Serve warm with extra ranch or chipotle sauce on the side if desired. Enjoy!