Preheat oven to 375 degrees
Brush two standard size the muffin tins (6 cups per tin), with olive oil
In a large bowl, whip the eggs and cream, then stir in the zest, salt and pepper.
Heat olive oil in a pan over a medium burner. Saute the onion until soft, about 4 minutes.
Add arugula to the pan. It will look like a lot, but it will wilt down. Sauté arugula until it is wilted, but still bright green. Immediately remove arugula and onions from the pan so the arugula does not continue to cook.
Evenly disperse the arugula/onion mixture among the 12 muffin tin cups. Top them with an equal portion of the chopped lox.
Add approximately 3 & ½ Tbs of the egg mixture to each muffin cup. I used a ¼ measuring cup to ladle the eggs, but did not fill it completely.
Bake for 20 minutes, or until firm, puffed, and lightly browned.
Let the frittatas rest for 5 minutes, and then remove them to a serving plate. If they stick to the muffin cups, run a small sharp knife around the perimeter of the frittatas, to free them.
Serve hot or warm.
Keep leftovers in the refrigerator covered for up to 5 days. To reheat, place frittatas on a microwave safe plate and heat for a minute on high, or until heated through.