Preheat your oven to 400°F (200°C).
Wash and dice the russet potato into small 1/2-inch cubes.
Toss the potato cubes with half of the avocado oil and a pinch of sea salt on a parchment-lined baking sheet.
Roast the potatoes for 20-25 minutes, flipping halfway through, until they are golden and crispy.
While the potatoes roast, slice the red bell pepper into thin strips.
Season both sides of the sirloin steak with the remaining sea salt, black pepper, and garlic powder.
Heat a cast-iron skillet over medium-high heat with the remaining avocado oil.
Sear the steak for 3-4 minutes per side for medium-rare, or until it reaches your desired level of doneness.
Remove the steak from the pan and let it rest on a cutting board for 5 minutes.
In the same skillet, add the bell pepper strips and sauté for 3-5 minutes until they are tender and slightly charred.
Slice the steak against the grain and serve it alongside the roasted potatoes and sautéed peppers.