Toast the walnuts in a dry skillet over medium heat, shaking frequently, until fragrant and lightly browned, about 4–5 minutes. Transfer to a plate to cool, then coarsely chop.

Prep fruit & vegetables

Wash and dry the grapes and greens. Halve the grapes. Core and dice the apple into roughly 1/2-inch pieces; toss the apple pieces with 1 teaspoon lemon juice (from the dressing amount) if you want to prevent browning. Thinly slice the celery and green onions. Chop the tarragon leaves.

Combine main salad components

In a large bowl, place the shredded/chopped cooked chicken, halved grapes, diced apple, sliced celery, green onions, and toasted walnuts. Add the crumbled blue cheese and chopped tarragon, reserving a small sprinkle of blue cheese and a few walnut pieces for garnish if desired.

Dressing

Whisk together the mayonnaise, Greek yogurt, lemon juice, Dijon mustard, honey, salt, and black pepper in a small bowl until smooth and well combined. Taste and adjust seasoning—add up to 1 teaspoon more honey for sweetness or a pinch more salt if needed.

Fold half of the dressing into the chicken mixture first to moisten, then add more as needed until the mixture is lightly coated but not soggy. You may not need all the dressing; reserve extra in the refrigerator for another use.

Assembly & Serve

Warm the croissants briefly in a 350°F (175°C) oven for 5–7 minutes if desired, or slice them horizontally without toasting for a softer presentation.

On each croissant base, place about 1 cup of mixed salad greens. Spoon approximately 3/4 to 1 cup of the dressed Chicken-Waldorf mixture onto the greens. Sprinkle the reserved blue cheese and walnut pieces over the top, and add a small sprig of tarragon or a few extra green onion slices for garnish.

Close the croissant, serve immediately, and pass extra dressing on the side if desired.