Preheat a grill. In a small saucepan, boil cider until thickened and reduced to 2 to 3 tablespoons. Remove from heat, and let cool; set aside.
In a meat grinder fitted with a 3/8-inch plate or a food processor fitted with the metal blade, coarsely grind chicken thighs. Transfer to a large bowl. Add reduced apple cider, apples, salt, pepper, sage, ginger, cinnamon, nutmeg, and dissolved bouillon. With your hands, knead mixture until well blended. Form a small patty, and grill until cooked through. Taste, and adjust for seasoning.
Divide sausage mixture into 7 or 8 portions (each about 1/2 pound). Grill sausage patties over medium heat for 3 minutes per side. Cut into a patty to test, there should be no pink showing. Alternatively, wrap patties tightly in plastic wrap and refrigerate or freeze for later use. The sausage will keep in the refrigerator for 3 days, or for 2 months in the freezer.
Place sausage patties on buns and top with tomatoes, lettuce, mayonnaise, and bacon. Serve with slaw on the side, if desired.