Pat the sirloin steak dry with paper towels and season both sides evenly with sea salt, black pepper, and garlic powder.
Heat half of the olive oil in a large 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, or until it reaches your desired level of doneness.
Remove the steak from the skillet and let it rest on a cutting board for at least 5 minutes to keep the juices intact.
While the steak rests, add the remaining olive oil to the same skillet and toss in the broccoli, bell peppers, and zucchini.
Sauté the vegetables for 5-6 minutes, stirring occasionally, until they are tender-crisp and slightly charred.
Slice the rested steak against the grain into thin, bite-sized strips.
Divide the cooked quinoa into a bowl, top with the sautéed vegetables, and finish with the seared steak strips.