Step 1: Roast the Poblanos. Preheat your oven to 400°F (200°C). Place the poblano peppers on a roasting pan and roast for 20-25 minutes, turning occasionally until the skin is blackened and blistered.
Step 2: Peel and Prepare the Peppers. Place roasted poblanos in a sealed plastic bag for 10 minutes to steam. Peel off the skins, slit the peppers, and remove the seeds.
Step 3: Prepare the Filling. Slice Oaxacan cheese and Queso Fresco into strips. Stuff each pepper with equal amounts of cheese.
Step 4: Make the Batter. Beat egg whites until soft peaks form. In another bowl, whisk egg yolks, flour, and salt. Fold in the beaten egg whites.
Step 5: Fry the Peppers. Heat vegetable oil in a frying pan. Dip stuffed poblano in batter, then fry for 3-4 minutes on each side until golden.
Step 6: Serve and Garnish. Serve fried Chile Rellenos topped with crumbled Cotija cheese and chopped cilantro.