Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Peel and dice the sweet potato and carrots into uniform 1/2-inch cubes to ensure even cooking.
In a medium bowl, toss the diced vegetables with half of the olive oil, rosemary, and a pinch of the sea salt and black pepper.
Spread the vegetables in a single layer on the baking sheet and roast for 20-25 minutes until tender and slightly caramelized.
While the vegetables roast, season the diced sirloin with garlic powder and the remaining sea salt and black pepper.
Heat the remaining olive oil in a heavy-bottomed skillet over medium-high heat until shimmering.
Add the beef to the skillet and sear for 4-5 minutes, turning occasionally, until a deep golden crust forms on all sides.
Add the fresh spinach to the skillet and sauté for 1 minute until just wilted and vibrant green.
Toss the roasted root vegetables into the skillet with the beef to combine all the savory juices before serving warm.