To keep this skillet strictly keto, choose fresh Mexican chorizo without added sugars or fillers and use full fat cheese and dairy. The optional onion adds flavor but also a small amount of carbs, so reduce or omit it if your daily carb allowance is very low. The eggs will continue to cook from residual heat after you turn off the burner, so remove the skillet while they are still slightly soft to avoid overcooking. This dish reheats well in a skillet over medium low heat, and you can refresh leftovers with a sprinkle of extra cheese or a drizzle of olive oil for added richness. Store cooled portions in airtight containers in the refrigerator for up to 4 days, and avoid freezing to preserve the best egg texture.