Dice onions to desired size. Add to medium sauce pan over medium heat with melted butter.
Cook onions until soft and tender. Remove from heat and place in small bowl.
Add grilled chicken to medium sauce pan over medium heat and season to desire.
Remove chicken from heat and place in bowl.
Scramble and season eggs to desire.
Remove from heat and place in bowl.
Spray pan with cooking spray.
Add handfuls of cheddar cheese to pan spread out evenly.
Let cheese melt and bubble. Use a spatula to check underneath. When cheese becomes light brown underneath, lift pan and drain cheese oil into small bowl.
After draining cheese oil, remove cheese shell from pan and place on plate.
Use spatula and fold from flat to taco shell shape. (Use a taco shell holder if you have one)
Build taco to desire with chicken, eggs, and onions.
