| Mushrooms, onion, peppers, leeks Thin, even dice or slices; dry before they go in | First, in the pan, before the eggs | Cook 3–6 minutes until soft and the pan is dry, then remove with the pan wiped. |
| Spinach, chard, kale, tomatoes Chop; squeeze cooked spinach dry | First, wilted, then returned at the fold | Wilt in the hot pan for a minute and press out the water or the omelet turns watery. |
| Potatoes (Spanish tortilla) Slice thin; par-boil or cook slowly in oil | First, cooked tender, then stirred into the egg | Raw potato never softens inside an omelet. Cook it until a knife slides through. |
| Chicken, shrimp, beans, leftover grains Already safely cooked; cut small; pat dry | Warmed through with the fillings, then lifted out | Poultry and leftovers reheat to 165°F / 74°C; shellfish to 145°F / 63°C. |
| Grated cheese Fine grate; one tablespoon is plenty | Last 30 seconds, on the egg before folding | Added early it sinks and browns; added late it melts into the egg. |
| Fresh herbs, scallions, pepper Chopped; a little set aside for the top | Whisked in, or scattered after cooking | Delicate herbs lose flavor under heat — stir half through the egg, finish with the rest. |
| Avocado, cucumber, fresh salsa, smoked salmon Sliced or spooned ready | After cooking, inside the fold or on top | These go limp or weep if cooked, so they only ever meet a finished omelet. |
| Bacon, ham, sausage, chorizo Crisp and drain first; skip where you can | Crisped before the eggs, added at the fold | Highest sodium and saturated fat in the pan — herbs, citrus and pepper flavor eggs for free. |