Tuna Noodle Casserole

Name: Tuna Noodle Casserole
Ingredients: 1 medium onion, finely chopped; 4½ tablespoons unsalted butter; 10 oz. mushrooms, trimmed and sliced ¼-inch thick (4 cups); 2 teaspoons soy sauce; ¼ cup sherry; ¼ cup all-purpose flour; 2 cups low-sodium chicken broth; 1 cup whole milk; 2 teaspoons fresh lemon juice; ¼ teaspoon salt; 1 (6-oz.) can tuna in olive oil, drained; 6 oz. dried curly egg noodles (preferably Pennsylvania Dutch–style; about 3¼ cups); 1½ cups coarse fresh breadcrumbs (from 3 slices firm white sandwich bread); 4 oz. coarsely grated cheddar (1 cup); 1 tablespoon vegetable oil