Flax-Crusted Tuna Burgers

1 pound fresh or frozen skinless tuna fillets

1 egg white

1/4 cup dry whole-wheat bread crumbs

1 tablespoon snipped fresh tarragon

1/4 teaspoon salt

1/4 teaspoon ground black pepper

1 tablespoon flaxseed

Nonstick cooking spray

1 medium avocado, halved, seeded and peeled

2 tablespoons light mayonnaise

1/2 teaspoon finely shredded lemon peel

1 tablespoon lemon juice

1  clove garlic, minced

1/8 teaspoon salt

2 whole-grain or whole-wheat sandwich thins, split and toasted

1 cup fresh spinach leaves

4 slices tomato

To Make

To prepare Flax-Crusted Tuna Burgers: Thaw tuna, if frozen. Rinse tuna; pat dry with paper towels. Finely chop tuna and set aside. In a medium bowl beat egg white with a fork. Stir in bread crumbs, tarragon, the ¼ teaspoon salt and ⅛ teaspoon of the pepper. Add tuna; stir gently to combine. Shape mixture into four ½-inch-thick patties, using damp hands if necessary.

In a shallow dish combine the flaxseed meal and flaxseeds. Dip tuna patties into flaxseed mixture, turning to coat evenly. 

Coat a large nonstick skillet or nonstick griddle with cooking spray. Heat over medium heat. Add tuna patties; cook for 10 to 12 minutes or until an instant-read thermometer inserted into sides of patties registers 160°F, turning once halfway through cooking time.

Meanwhile, prepare Avocado Aioli:

In a medium bowl use a potato masher or fork to coarsely mash avocado. Add mayonnaise, lemon peel, lemon juice, garlic, the ⅛ teaspoon salt and the remaining ⅛ teaspoon pepper. Continue to mash until mixture is well mixed but still slightly chunky.

To serve, place one sandwich thin half, cut side up, on each of four serving plates. Top with spinach leaves and tomato slices. Top each with a cooked tuna patty. Spoon one-fourth of the avocado mixture over each patty.