Slice chicken breasts in half, lengthwise, to halve the thickness. Place in bowl or ziplock bag with 1/2 cup of dijon. Marinate in the refrigerator 8 hours, or (if less) as long as you can. **I've done this without marinating and it's good, just not quite as flavorful.
In a bowl mix together the mayonnaise, the garlic salt, the pepper, and the 4 tablespoons dijon. Dip each chicken breast half in mixture.
On a plate place two strips of bacon in an X. Roll up the chicken breast half starting with the small end (like a backwards crescent roll). Wrap the bacon around the roll, make sure it is snug, secure in the center with toothpick. Repeat with remaining 3 pieces of chicken.
Place each chicken bundle in baking dish. Spoon any remaining mayo/dijon mixture over the top.
Bake for 45 minutes, or until juices run clear, or internal chicken temp is 165*. Broil briefly to crisp bacon.