Preheat oven to 400°F. Mix ground beef, milk, breadcrumbs, parmesan, eggs, onion, garlic, salt, pepper, fennel, Italian seasoning, basil, red flakes, and parsley—just until combined. Spread half the marinara in a 9x13 dish, shape meat into a loaf on top, cover with foil, bake 45 minutes. Uncover, add rest of sauce and mozzarella, bake 15 more. Cool a bit, top with basil, slice. Done.