Preheat oven to 375 degrees and spray an 8x8 baking dish with cooking spray.
Heat oil in a large frying pan over medium-high heat. Add spinach and sauté until bright green and wilted, about 4-5 minutes. Spread cooked spinach into an even layer in baking pan.
In a medium bowl, whisk together eggs, salt, pepper, oregano and garlic powder. Pour mixture over spinach and use a fork to carefully stir the spinach and eggs. Sprinkle entire dish evenly with crumbled feta.
Bake in oven until eggs are fully cooked through, about 30-35 minutes. Slice pan into eight pieces to serve.