Remove the skin from the chicken and carefully carve the bone away from the breast meat. Thinly slice the breast crosswise on the diagonal.
Evenly spread the honey mustard on 1 side of each bread slice. Lay 3 to 4 slices of tomato on 2 slices, followed by some endive and half the chicken on each. Season the layers with salt and pepper, to taste, as you build the sandwich. Top each sandwich with the other dressed bread slice.
Serve immediately or wrap and refrigerate until ready to eat.