Position a rack in the center of the oven and heat the oven to 450°F.
Cut off the narrow top portion of the squash close to where it widens (reserve the base for another use). Peel and slice it into 12 thin (about 1/4-inch) rounds.
Brush both sides of the squash with 1 Tbs. of the oil and spread in a single layer on a large rimmed baking sheet. Sprinkle with the rosemary, 1/2 tsp. salt, and 1/2 tsp. pepper. Roast, turning once, until softened and browned, about 25 minutes.
Meanwhile, in a 12-inch skillet, cook the bacon over medium heat, stirring occasionally, until crisp, 5 to 7 minutes. Transfer with a slotted spoon to paper towels to drain.
In a small bowl, whisk together the vinegar, mustard, 1/2 tsp. salt, and 1/2 tsp. pepper. Slowly whisk in the remaining 4 Tbs. oil and season with more salt and pepper to taste.
In a large bowl, toss the escarole and pears with enough of the vinaigrette to coat lightly. Season to taste with salt and pepper. Arrange the squash on 4 large dinner plates. Top each with a mound of the escarole and pears and sprinkle with the bacon. Tuck 2 wedges of Stilton into each salad and serve.