Preheat oven to 400 degrees.
Fill a large stock pot with water and bring to a boil. Add the shells and cook, stirring to make sure the pasta shells don't stick. Cook until slightly al dente. Remove shells from pot and set aside to cool before filling.
Meanwhile, preheat a skillet to medium-high heat. Add olive oil, ground chicken, Djon, salt, and pepper. Cook the chicken until no longer pink about five minutes. Remove from skillet and set aside. In the same skillet, melt the butter. Whisk in the flour and stir until a roux forms. Gradually add the milk and continue to stir until thickened. Remove skillet from heat and add in the the ground chicken, 1 cup Gruyere, salt, pepper, and stir to combine.
Spray an 8X5 baking dish with non-stick cooking spray. Take about one tablespoon of the chicken filling and put it inside the shell. Repeat until all shells have been use. You may have extra filling leftover. Top the shells with remaining 1/2 cup Gruyere, cover the top with foil, and bake for about 25 minutes. Remove from oven and garnish with fresh chives and crispy prosciutto.
Spray a small baking sheet with non-stick cooking spray. Place slices of prosciutto on the baking sheet. Cook for about 3 to 5 minutes at 400 degrees or until crispy. Remove from oven, cool, and then chop.