Seed and clean chilies, cut in half -- lengthwise. Place on a cookie sheet -- with one chili half across from another on the sheet so there is a top and a bottom.
Beat eggs in a shallow bowl and set aside.
In another shallow bowl, season flour to your taste with the garlic powder and salt and pepper.
Dip each half of chili into the beaten egg and then dredge the chilie on the outside only into the flour, and put back onto the cookie sheet.
After the egg and flour step is completed; put a good amount of cheese on all of the bottoms of the chilies and then top with onion. (If you have 10 halves on the sheet you will put the cheese and onions on 5 of the halves.)
Flip the chili half that does not have the cheese and onion on it ontop of the filled chili half. Then put the cookie sheet into the refrigerator for at least 30 minutes before frying the rellenos.
Just before you are ready to serve the rellenos you need to fry them. I have found it easier to use a double spatula and a single one -- one in each hand. Using this method helps keep the relleno together when you put them into pan and flip them to fry the other side.
We top the rellenos with El Pato sauce at the table.