Seared Tuna Sandwich with Balsamic Onions

Ingredients

• 2 teaspoons butter
• 2 cups vertically sliced onion
• 1 1/2 tablespoons balsamic vinegar
• 1/4 teaspoon dried thyme
• 1 tablespoon all-purpose flour
• 1/2 teaspoon salt
• 1/4 teaspoon garlic powder
• 1/4 teaspoon black pepper
• 4 (6-ounce) tuna steaks (about1/2 inch thick)
• Cooking spray
• 4 teaspoons Dijon mustard
• 4 (2-ounce) whole wheat hamburger buns
• 4 curly leaf lettuce leaves
• 4 (1/4-inch-thick) slices tomato

Preparation

1. Melt butter in a medium skillet over medium-high heat. Add onion; sauté 5 minutes. Stir in vinegar and thyme; cover and cook 5 minutes, stirring occasionally.
2. While onion cooks, combine flour, salt, garlic powder, and pepper in a shallow dish. Dredge fish in flour mixture. Heat a large nonstick skillet coated with cooking spray over medium-high heat. Add fish; cook 3 minutes on each side or until desired degree of doneness.
3. Spread 1 teaspoon mustard over top half of each bun. Layer 1 lettuce leaf, 1 fish steak, 1 tomato slice, and 1/4 cup onion mixture on bottom half of each bun. Top with top halves of buns.