Preheat your oven to 425°F for the potatoes and green beans.
Chop the red potato into small cubes and toss with olive oil, salt, and pepper. Spread evenly on a baking sheet.
Roast the potatoes in the oven for about 20-25 minutes, stirring halfway through until golden and tender.
While the potatoes roast, trim the ends of the green beans and toss them lightly with salt, pepper, and a drizzle of olive oil. Add them to the baking sheet during the last 10 minutes of the potato roasting process.
Season the sirloin steak with salt and pepper on both sides.
Heat a skillet over medium-high heat. Add the olive oil and once hot, sear the steak for about 3-4 minutes per side for medium-rare, adjusting time based on your preferred doneness.
In the last minute of cooking, add the minced garlic (from 2 cloves) and the unsalted butter to the pan, spooning the melted garlic butter over the steak.
Remove the steak from the skillet and let it rest for a few minutes before slicing.
Serve the steak alongside the roasted potatoes and crispy green beans, drizzled with any remaining garlic butter from the pan.