In a bowl, combine ingredients for the filling and toss together, set aside.
Heat an 8" skillet over medium-low heat. Add 1 teaspoon olive oil, swirling until the bottom of the pan is covered.
Whisk together the eggs, milk, and salt. Pour half the mixture into the hot skillet. As the bottom of the eggs set, lift up the side of the eggs with a spatula and let uncooked eggs run under the cooked eggs. Continue until egg is fairly well set. Carefully flip the omelette over and sprinkle in half the mixture. Turn off heat, fold omelette in half, and allow to sit for 1-2 minutes until cheese warms. Transfer to a plate and repeat with remaining eggs. Sprinkle with parsley and feta before serving.
Notes
+ The feta and olives are fairly salty which leads me to be conservative with the salt amount.