Cook the chicken breast using your preferred method—whether baking, poaching, grilling, or pan-searing—until it reaches an internal temperature of 165°F (74°C). Using a meat thermometer is the best way to ensure the chicken is safely cooked without becoming dry. Once cooked, transfer the chicken to a plate and let it rest for 5–10 minutes. This resting period helps retain the juices, keeping the chicken tender and flavorful. After it has cooled slightly, shred it using two forks or dice it into small, bite-sized pieces, depending on your preferred texture.

In a large mixing bowl, prepare the creamy high-protein dressing by combining the Greek yogurt, light mayonnaise, Dijon mustard, fresh lemon juice, garlic powder, onion powder, salt, and black pepper. Stir everything together until the mixture is smooth, creamy, and evenly blended. Taste the dressing and adjust the seasoning if needed by adding a little more lemon juice for brightness or an extra pinch of salt and pepper to enhance the flavor.

Add the diced celery, finely chopped red onion, halved grapes, chopped pecans, and fresh parsley to the prepared dressing. Gently stir the ingredients until they are evenly distributed throughout the mixture. The celery adds a satisfying crunch, the grapes provide a touch of sweetness, and the pecans contribute richness and texture that make every bite more enjoyable.

Add the shredded or diced chicken to the bowl with the dressing and vegetable mixture. Using a large spoon or rubber spatula, gently fold everything together until all of the chicken pieces are thoroughly coated in the creamy Greek yogurt dressing. Be careful not to overmix, as this can break down the chicken too much and affect the texture of the finished salad.

Cover the bowl tightly with plastic wrap or transfer the chicken salad to an airtight container. Refrigerate for at least 20–30 minutes before serving. This chilling time allows the flavors to meld together, resulting in a more flavorful and cohesive chicken salad. If you have extra time, chilling it for an hour will enhance the taste even further.

If desired, lightly toast the whole grain bread slices in a toaster, toaster oven, or skillet until they are lightly golden and slightly crisp. Toasting the bread not only adds extra texture and flavor but also helps prevent it from becoming soggy once the chicken salad is added.

Arrange lettuce leaves and tomato slices evenly over four slices of the prepared bread. The lettuce creates a fresh, crisp barrier that helps keep the bread from absorbing moisture, while the tomatoes add juiciness and a burst of fresh flavor.

Divide the chilled chicken salad mixture evenly among the prepared bread slices. Use the back of a spoon to gently spread the chicken salad into an even layer, ensuring each sandwich gets a generous portion of the creamy, protein-packed filling.

Place the remaining slices of bread on top to complete the sandwiches. Press down gently to help hold everything together, then use a sharp knife to cut each sandwich in half diagonally or straight down the middle, depending on your preference. This makes them easier to serve and enjoy.

Serve the sandwiches immediately while the bread is fresh and the filling is chilled. If meal prepping, store the chicken salad separately in an airtight container in the refrigerator for up to 4 days and assemble the sandwiches just before serving. This helps maintain the best texture and prevents the bread from becoming soggy during storage.