Preheat oven to 350°F (175°C). Line a baking sheet with foil.
Lightly brush chicken breasts with olive oil.
Mix Old Bay seasoning, garlic powder, onion powder, and celery salt in a small bowl.
Sprinkle the seasoning mixture generously over both sides of the chicken.
Bake chicken for 20-25 minutes, or until cooked through (internal temp 165°F/74°C).
Let chicken cool completely, then dice into small, bite-sized chunks.
In a large bowl, combine diced chicken, diced celery, diced onions, chopped eggs, and sweet relish.
Gradually stir in mayonnaise until the salad reaches your desired creamy consistency.