Preheat oven to 375°F (190°C) and grease a 9x13 dish.
Cook pasta until just al dente, drain.
Cook raw ground turkey if using, season lightly.
Dice cooked turkey, chop onion, mince garlic.
Mix soup, broth, sour cream in bowl; add onion, garlic, veggies, seasonings.
Fold in pasta and turkey, mix in 1.5 cups cheddar.
Spread mixture in baking dish, top with remaining cheese.
Combine breadcrumbs, butter, Parmesan; scatter over casserole.
Cover with foil, bake 25 min; uncover and bake 15–20 min until golden.
Rest 5–10 min before serving.