Spray a baking sheet with cooking spray. Preheat your oven to 400 degrees.
For meatballs: Combine ground beef, oats, egg, onion, milk, salt, pepper, Worcestershire, ketchup, and parsley in a large bowl. Mix well with clean hands or a spoon. Roll into 1 1/2 inch meatballs. (Use a cookie dough scoop to get uniform-sized meatballs.)
Arrange the meatballs in a single layer on the prepared pan and bake at 400° for 18-20 minutes, shaking the pan occasionally so they brown evenly. The internal temperature should be 160°.
While the meatballs bake, cook the pasta in boiling salted water and make the sauce.
For sauce: Melt butter in a large pot over medium heat. Whisk in the flour. Gradually add the broth and milk; stirring constantly. Bring to a boil; cook and stir for 2 minutes, or till slightly thickened. Stir in the thyme, parsley, salt, and pepper.
Drain meatballs on paper towels; then add them to the sauce. Stir gently until all the meatballs are coated.
Serve hot meatballs and sauce over cooked pasta.