Heat 1 1/2 teaspoons olive oil in an 8-inch cast-iron skillet over medium heat. Add onion; sauté 5 minutes or until tender. Remove from heat. Stir in green onions, thyme, and 1/4 teaspoon pepper. Remove onion mixture from the skillet; set aside.
Coat skillet with cooking spray. Combine the potatoes, remaining 1 1/2 teaspoons oil, and remaining 1/4 teaspoon pepper. Press potato mixture into the bottom of skillet. Broil 15 minutes or until potatoes are crisp and golden.
Reduce the oven temperature to 375°.
Spread the onion mixture over the potato mixture; sprinkle with salmon, cheese, and salt. Pour egg substitute over the top. Bake at 375° for 38 minutes or until it is puffy and lightly browned.