Place tortillas on a flat work surface. Pile chicken, cheese and other fillings in the center "square" of each tortilla. Working one at a time, fold the right and left sides of each tortilla in toward the center, covering the outer edges of the filling by about 1"; hold in place while folding the edge closest to you away from you, up and over the filling to cover. Press and hold these three sides firmly against the filling as you roll the burrito away from you toward the top edge. Set aside, seam side down, while you shape the other burritos. Brush the outside of tortillas lightly with olive oil. Cook, seam side down, on a grill pan preheated to medium-high until filling is hot and tortilla is slightly crispy and covered with grill marks, flipping 1-2 times (4-5 min. total). Serve with desired garnishes.
Note: Burritos can also be grilled in a panini press or countertop grill (such as a George Foreman Grill); flipping not required.