If going directly into the oven, preheat oven to 350 degrees.

Heat 1 Tbsp oil in a heavy, oven-safe skillet. (If you don’t have an ovenproof skillet, use a 9" x 13" casserole dish.) Add washed and slightly wet spinach to the pan then cover and steam for 2–3 minutes. Lift cover and stir spinach with a wooden spoon. Cover and steam for an additional 2 minutes until all the spinach has wilted. Don’t overcook.

Remove spinach from skillet then drain in a colander, making certain to squeeze out the water with a large spoon. Set aside.

Add remaining oil to skillet and heat until it shimmers. Add onion to skillet then cook until translucent about 3 minutes. Remove from heat.

Separate spinach with two forks. Sprinkle separated spinach over the onion. The spinach will try to clump up, so keep separating it until it’s mixed together.

Sprinkle top of the spinach evenly with Parmesan cheese.

Whisk eggs in a large bowl until smooth. Add remaining ingredients (except feta) then whisk until blended. Pour mixture into skillet. Sprinkle the top with the crumbled feta.

Place skillet in oven and bake for 30–35 minutes or until the middle is set and bounces back to touch or a knife inserted into the middle comes out clean.