Preheat oven to 400 degrees F. Soak sliced potatoes in cold water for at least five minutes. Pat dry on kitchen towels.
In a medium bowl, swirl together oil, oregano, garlic powder, salt, and pepper. Toss potatoes and onions to coat. (I toss them around with my hands to make sure all sides of the potatoes are covered with seasoning.)
Spread potatoes and onions in an even layer on a baking sheet lined with a silicone mat or parchment paper. Bake in preheated oven for 20-30 minutes, until potatoes are bubbly and browned.
While potatoes cook, heat oil in a medium skillet. Whisk in flour until smooth. Whisk in broth a little at a time, making sure mixture is smooth before adding more liquid.
Add onion powder and garlic powder to gravy, and continue to simmer until thickened. Add sliced beef, and gently stir to cover. Serve beef and gravy over potatoes when done.