Tuna Caesar Sandwiches

Ingredients

• 2 cans (5 ounces each) white water-packed tuna, drained and flaked
• 1/4 cup marinated quartered artichoke hearts, drained and chopped
• 1/4 cup finely chopped onion
• 1/4 cup reduced-fat mayonnaise
• 3 tablespoons grated Parmesan cheese
• 2 teaspoons lemon juice
• 1 teaspoon Dijon mustard
• 8 slices whole wheat bread, toasted
• 16 cucumber slices
• 8 slices tomato
• 2 cups shredded lettuce