Preheat oven to 400 degrees. Grease or spray with non-stick cooking spray an 8"x8" baking dish. Set aside.
In a medium skillet over medium heat melt butter. Add in diced onion and saute until softened. Cut hotdogs into 1/2 inch pieces and add to softened onion.
Cook until hotdogs are crispy around edges and heated through for 5 minutes. Lower heat to low and stir in mustard until all hotdogs are coated. Turn off heat.
In medium bowl whisk together corn muffin mix, milk, egg, green chilies, 1/2 (4oz) cheddar cheese. Using a spatula mix in 3/4 of the cooked hotdogs & onions.
Pour mixture into a prepared 8" x 8" baking dish. Top with remaining hotdogs and onions. Sprinkle remaining (2oz) shredded cheddar cheese on top.
Bake in preheated oven for 20 minutes until cornbread mixture is done. Test in center with a toothpick. Garnish with sliced green onions. Serve along side of ketchup and mustard. Enjoy with French Fries.