Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Dice the russet potato into 1/2-inch cubes and slice the bell peppers into thin strips.
In a large bowl, toss the potatoes and peppers with half of the olive oil, half of the sea salt, half of the black pepper, and all of the smoked paprika.
Spread the vegetables in a single layer on the prepared baking sheet and roast for 20-25 minutes until the potatoes are tender and golden-brown.
While the vegetables roast, season the sirloin steak on both sides with the garlic powder and the remaining sea salt and black pepper.
Heat the remaining olive oil in a cast-iron skillet over medium-high heat until shimmering.
Place the steak in the hot skillet and sear for 3-4 minutes per side for medium-rare, ensuring a deep brown crust forms.
Remove the steak from the pan and let it rest on a cutting board for 5 minutes before slicing against the grain.
Serve the sliced steak alongside the roasted potatoes and peppers for a complete, clean-eating meal.