Heat one tablespoon of olive oil in a 10-inch cast iron skillet over medium heat. Add the leek, shallot and scallions and saute for 1-2 minutes, or until slightly translucent. Then, remove the vegetables to a plate and set aside.
In a large mixing bowl, add the eggs and yogurt and whisk together. Stir in the herbs, smoked salmon, goat cheese, sauteed leek, shallot and scallions, salt and pepper.
Once your skillet has cooled, clean it (or use a paper towel to quickly wipe it clean). Over low heat, add two tablespoons of olive oil to the skillet and ensure that the bottom is full coated.
Pour the frittata egg mixture into the skillet and cook for 8-10 minutes, or until the sides are just starting to set.
Transfer the frittata to the oven (on a middle shelf) and turn the top broiler on. Continue cooking for another 8-10 minutes, checking on it every few minutes to ensure the top isn't browning too much. If the top cooks faster than the inside of the frittata, turn the broiler off and let it continue cooking in the oven.
Serve the frittata with extra herbs.