Roast the Potatoes: Preheat oven to 425°F. Toss diced potatoes with olive oil, rosemary, garlic powder, salt, and pepper. Spread on a baking sheet and roast for 25–30 minutes, flipping halfway, until golden and crispy.
Make the Chimichurri: In a bowl, combine parsley, oregano, garlic, red wine vinegar, olive oil, red pepper flakes, salt, and pepper. Mix well and let sit for at least 10 minutes.
Cook the Steak: Pat steak dry and season with salt, pepper, and garlic powder. Heat olive oil in a skillet over medium-high heat. Cook 4–5 minutes per side for medium-rare. Let rest 10 minutes, then slice thinly against the grain.
Sauté the Vegetables: In a skillet over medium heat, add olive oil and cook sliced peppers and onions with a pinch of salt for 5–7 minutes until soft and slightly caramelized.
Assemble the Bowl: Add roasted potatoes to one side of the bowl, sautéed peppers and onions to another, and sliced steak in the center. Spoon chimichurri generously over the steak. Serve immediately.