Heat. oven to 400°F. heat 2 tablespoon of oil in a large oven-proof non-stick skillet over medium. heat.

Add the potato and onion and cook, tossing occasionally until the potato red tender. 12-15 minutes

Meanwhile in a large bowl whisk together the eggs, half teaspoon salt and quarter teaspoon pepper. Mix in the spinach, Cheddar and ham.

Add the egg mixture to the skillet stir in once, and transfer the skillett to oven. Cook until the eggs are set 12-14min.

Meanwhile in a large bowl, whisk together the vinegar, mustard, the remaining tablespoon. of oil and quarter teaspoon each salt and pepper. Add the lettuce. and toss to coat. Serve. with the frittata