Roast the peppers: Place poblano peppers directly over a gas flame or under a broiler, turning occasionally until skins are blistered and charred. Transfer to a plastic bag and let steam for 10 minutes.

Peel and prepare peppers: Carefully peel off the charred skin. Make a small slit lengthwise and remove seeds, keeping stems intact. Rinse gently if needed and pat dry.

Stuff the peppers: Cut cheese into thick strips or chunks. Carefully stuff each pepper with cheese, making sure not to overfill. Close the opening with toothpicks if needed.

Prepare the batter: Separate eggs. Beat whites until stiff peaks form. Gently fold in yolks, one at a time, along with a pinch of salt.

Fry the peppers: Heat oil in a deep skillet. Lightly coat each pepper in flour, then dip in egg batter. Fry until golden brown, about 2-3 minutes per side. Drain on paper towels.

Make the sauce: In a saucepan, sauté onion and garlic until soft. Add tomato sauce, cumin, oregano, salt and pepper. Simmer for 10 minutes. Serve chiles rellenos covered with sauce.