Thaw the Tribeca Oven Multigrain Loaf at room temperature for 1 hour. Cut 8 slices of bread that are about ¼” in width. Tip: For best sandwich results, cut the slices from the middle of the loaf. Set aside.
Butterfly the chicken breasts to create 4 thin pieces. Season with salt and ground black pepper, and thoroughly cook the chicken in a large skillet with some oil. Remove the chicken and set aside on a plate. Carefully wipe the skillet clean when done.
While the chicken is cooking, make the chipotle mayonnaise by adding the mayonnaise, chipotle pepper, and adobo sauce in a small food processor and blend until thoroughly mixed.
Thinly slice the red onion.
To build the sandwich, spread thin layers of the chipotle mayonnaise on all 8 slices of bread. Place the cooked chicken breasts on the bottom pieces of bread and top with the Pepper Jack cheese. On the tops of the bread add the thinly sliced red onion and ¼ cup of arugula, then bring the two parts of the sandwich together.
In the large skillet, add a pat of butter and toast the sandwiches on both sides until the cheese is melted, flipping once.