Preheat the oven to 375 degrees F with the oven rack in the lower third of the oven. Lightly grease a large baking dish (or a couple smaller ones–I baked two-thirds of my shells in a 10 1/2-by-7-inch baking dish, and froze the rest in a 7-by-5-inch baking dish).
Boil the pasta shells in generously salted water for 1 minute less than the package directs. Drain and remove the shells to a tray or baking sheet so they are spread out and do not stick to each other. Allow them to cool.
Heat the olive oil over medium-high heat in a skillet and add the celery, cooking for about 5 minutes, stirring occasionally until crisp-tender. Remove from the heat and add to a medium mixing bowl along with the shredded chicken breast, ricotta cheese, 1/4 cup of the mozzarella, the hot sauce, and the crumbled blue cheese.
Spoon the chicken mixture into the cooked pasta shells dividing the mixture evenly. I yielded 19 stuffed shells. Place the shells into the greased baking dish and drizzle the tops of the shells with the blue cheese dressing. Top the shells with the remaining 1/2 cup shredded mozzarella cheese.
Cover the baking dish with foil and bake for 15 minutes, then uncover and continue to bake another 10 minutes or until bubbly and heated through. Serve immediately.