While this recipe calls for poaching raw chicken breasts, you could easily just use leftover cooked chicken.
1 Set a 2-quart pot of well salted water over high heat. As the water heats to a boil, cut the chicken breasts into large (2 1/2-inch) chunks. When the water boils, add the chicken. Turn off the heat and cover the pot. Let sit for 15 minutes (time it) or more while you prepare everything else.
2 In a large bowl, mix the mayo, mustard, vinegar, paprika, Cajun seasoning and horseradish together. Mix in the eggs, celery, green pepper, green onion.
3 Using a slotted spoon, remove the chicken from the poaching water* and dice it. Mix it in with the remaining ingredients. Add salt and hot sauce to taste. Chill before serving.
Serve over butter lettuce or between two pieces of bread for a sandwich.
*The resulting poaching liquid is a light, salted chicken broth. You can save it and pour it into a cup and drink it as a light soup if you want.