In a medium bowl, beat together the eggs, salt, and heavy cream. Set aside.
In a 12-inch skillet (oven-proof) over medium-high heat, add 1/4 cup of olive oil. When the oil is shimmery, add the zucchini into the pan in a single layer. Toss in the oil, then allow squash to sit undisturbed for 2-3 minutes, or until lightly browned.
Toss the zucchini to brown the other side 2 minutes more. Set aside 2 Tbsp of the parsley and green onion. Add in the remaining herbs to the zucchini and toss to incorporate. When the parsley is bright green, add in the eggs. Reduce the meat to medium-low and cover with a lid for 3 minutes, or until the bottom half of the frittata is cooked.
Turn off heat and sprinkle the top with Parmesan cheese—the top won’t be fully cooked.
Turn oven on to BROIL. Transfer frittata to the oven and broil for 3 minutes, or until the top is cooked and the cheese has browned. Rotate the skillet handle midway through broiling to ensure even cooking.
Remove from oven and garnish with the remaining herbs, olives, and feta cheese.