In a 400°F oven, bake the turkey tenderloin in a small baking dish for 30-45 minutes, until it has reached an internal temperature of 165°F.
While that bakes, bring a large pot of water to a boil for the pasta and broccoli. Add the pasta and broccoli to the boiling water. Cook for 10 minutes.
Meanwhile, In a food processor or with a box grater, shred the cheddar cheese and set aside.
Drain the water from the pasta and broccoli and set it aside. In the same pot, melt the butter, sprinkle in the flour, and begin whisking to incorporate the two. Cook for 1-2 minutes until the flour turns a light brown color.
Slowly whisk in the 2 cups of skim milk until the consistency resembles a thin gravy. Stir in the diced onion, garlic, sun dried tomatoes, salt, pepper, and shredded cheese. Stir until all of the cheese is melted.
The tenderloin should be done by now, remove and chop into 1 inch pieces.
Stir the pasta, broccoli, and diced tenderloin into the cheese mixture and pour into a large casserole dish.
In a small bowl combine the parmesan cheese and panko breadcrumbs.
Top the casserole with the breadcrumb mixture and return it to the oven, broil for 5 minutes until golden brown.