If you haven't already, rinse and peel the char from your roasted Hatch green chiles. Pat dry.
Slice your block of cheese along the longest edge into four equal strips.
Lay each of your Hatch chiles flat on a cutting board. Slice one side of each pepper from top to bottom, making sure to keep the opposite side intact. Open the halves like a book. Add sliced cheese to the inside of the peppers and fold back over to cover. See the visual guide above for reference.
On a medium plate, combine flour, cumin and garlic powder. Dredge each side of each stuffed chile, tapping away excess. Set aside.
Separate the eggs, placing the whites in a medium mixing bowl and the yolks in a smaller bowl.
Beat the egg whites with an electric mixer until stiff peaks form. You want these peaks to be very stiff! When you can turn your mixing bowl upside down and nothing falls out, you're done.
Whisk the yolks, baking powder and salt together. Using a flat spatula and as few motions as possible, gently fold egg yolks into the whites until just combined. Stirring too much will cause your batter to "fall" and become runny, so be easy!
Pour about half an inch of canola, vegetable, or other cooking oil into a frying pan. Heat over medium-high heat until shimmering.
Dip each chile in the batter, making sure to cover them completely. Place the dipped chiles in the oil, making sure not to overcrowd the pan. Fry for 2-3 minutes or until golden brown; flip and cook for another 2-3 minutes. Serve immediately.