Tuna-Filled Shells

Ingredients (12)

• 12 jumbo pasta shells
• 5 teaspoons all-purpose flour
• 2 cups 2% milk
• 1 teaspoon dill weed
• 1/2 teaspoon salt
• 1 celery rib, diced
• 1 small onion, diced
• 1 tablespoon canola oil
• 2 slices white bread, crumbled
• 1 can (12 ounces) light water-packed tuna, drained and flaked
• 1/2 cup reduced-fat ranch salad dressing
• 1/2 cup shredded part-skim mozzarella cheese