Wash and cube potatoes into 1/2-inch pieces and pat dry to ensure crisping.
Cut beef into 1-inch cubes and season with salt and pepper.
Heat 2 tablespoons of olive oil in a large skillet over medium-high heat.
Add potatoes to the skillet in a single layer and cook for 10-12 minutes, stirring occasionally, until golden brown and tender.
Remove potatoes from the skillet and set aside on a plate.
Add the remaining 1 tablespoon of olive oil to the same skillet and increase heat to high.
Add beef cubes in a single layer and sear for 2 minutes per side until a crust forms. Work in batches if necessary to avoid crowding.
Reduce heat to medium and add the butter, minced garlic, oregano, and red pepper flakes to the skillet.
Toss the beef in the melting garlic butter for 1 minute until the garlic is fragrant.
Return the cooked potatoes to the skillet and toss everything together to coat in the garlic butter sauce.
Garnish with fresh parsley and serve immediately.