Thaw the frozen croissants according to instructions and bake them till golden brown.
Meanwhile cut the chicken breasts into thin slices or strips. Rub with lemon pepper, or chipotle mango powder or any spices of your choice. (I used chipotle mango powder from Costco)
Add some olive oil and roast or broil them in the oven till done. Remove from the oven and let it cool down to room temperature.
Slice the tomatoes, wash, towel dry the lettuce and keep aside.
When the croissants cool down a bit, slice them in the centre with a bread knife more than half way through, without separating the two slices.
Spread some mayo & dijon mustard lightly on the inside, add the chicken then top with Swiss cheese, tomato slices and lettuce.
Drizzle some ketchup to the chicken if you want, just a little. Now close the sandwich and serve for lunch with some garden salad. You may also wrap it with cling wrap and pack it for lunch. The Croissant Sandwich is ready to go!