Garlicky Shrimp Alfredo Bake

penne

butter, divided

garlic, minced

medium or large shrimp, peeled and deveined

chopped fresh parsley, divided

all-purpose flour

milk

low-sodium chicken broth

shredded mozzarella, divided

plus 2 tbsp. freshly grated Parmesan, divided

Freshly ground black pepper

large tomatoes, chopped (about 1 c.)