Cut tops off peppers and remove seeds and white membrane to create cups.
In medium skillet, cook sausage, breaking up into small pieces as it cooks, until no pink remains. Drain off any excess fat. In the same pan, add olive oil and heat on medium heat. Add fennel, celery, and onion and cook until soft. Mix in sage, salt, and pepper followed by dry bread cubes. Toss to coat. Gradually add stock, 1/4 cup at a time until absorbed. Stuffing should be moist, but not wet.
Fill pepper cups with the stuffing. Place on cookie sheet sprayed with nonstick spray and bake for 15 to 20 minutes or until peppers are soft and the stuffing tops are lightly browned and crunch. Allow to rest for 5 minutes before serving.