1. Cook and Shred the Chicken
Boil or poach the chicken until fully cooked, about 15–20 minutes. Let it cool, then shred to yield roughly 3 cups.
2. Prepare the Dressing
In a medium bowl, mix together mayonnaise, Dijon mustard, and a pinch of salt and pepper until smooth.
3. Combine the Chicken Salad
Add the shredded chicken, celery, and green onions to the dressing. Stir gently until everything is evenly coated.
4. Assemble the Croissants
Slice each croissant horizontally. Spoon the chicken salad onto the bottom halves, then top with the remaining halves.
5. Serve or Store
Serve immediately for the best texture, or store in an airtight container in the fridge for up to 2 days.