Boil rotini in water, according to package directions. Drain, and rinse with cold water to cool it down. Place in mixing bowl, or in the bowl that you plan to serve the tuna pasta salad in. Set aside.
In a small mixing bowl, add mayo and vinegar.
Next, pour in garlic powder, sugar, seasoned salt, and black pepper.
Stir to combine mayo and vinegar mixture with spices.
Pour mayonnaise mixture over pasta.
Add tuna, celery, and green onion.
Stir until fully combined and mixed together. Serve!