Preheat and Set Up: Heat the oven to 400°F. Place the split rolls cut-side up on a baking sheet.
Make Herb Mayo: Stir the light mayonnaise and herb paste together in a small bowl until smooth.
Spread the Rolls: Spread the herb mayo on the cut sides of all roll halves.
Assemble the Sandwich Halves: Divide the shredded chicken among the bottom halves. On the top halves, add about 1 cup of the sliced mushrooms and the spinach, then top each with a slice of Swiss cheese.
Bake Until Toasted and Melty: Bake until the cheese melts and the rolls are lightly toasted, about 8 to 10 minutes.
Close the Sandwiches: Remove the pan from the oven and place the cheesy tops onto the chicken bottoms to form sandwiches.
Cook the Bacon: In a skillet over medium heat, cook the chopped bacon until browned and crisp, about 6 to 8 minutes. Use a slotted spoon to transfer bacon to paper towels.
Manage the Drippings: Carefully pour off excess bacon fat if there’s a lot, leaving about 1 tablespoon in the skillet for flavor.
Sauté the Remaining Mushrooms: Add the remaining 1 cup sliced mushrooms to the skillet and cook over medium heat until softened, about 4 to 5 minutes.
Warm the Dressing: Stir the spinach salad dressing into the skillet with the mushrooms and warm it for about 1 minute.
Toss the Warm Nappa Salad: Put the shredded nappa cabbage in a large bowl. Pour the warm mushroom-and-dressing mixture over it, add the cooked bacon and crumbled blue cheese, and toss until lightly wilted and coated.
Serve: Plate each sandwich with a generous scoop of warm nappa salad and eat while everything’s still warm and smug about it.