Preheat your oven to 400°F (200°C).
Dice the Yukon gold potato into 1/2-inch cubes and toss them in a bowl with half of the olive oil, half of the sea salt, and half of the garlic powder.
Spread the potatoes in a single layer on a parchment-lined baking sheet and roast for 20-25 minutes until golden-brown and crisp.
While potatoes roast, cut the chicken breast, beef sirloin, red bell pepper, and red onion into uniform 1-inch pieces.
Thread the meat and vegetables onto skewers, alternating between the chicken, beef, pepper, and onion pieces.
Whisk the remaining olive oil, oregano, remaining salt, pepper, and garlic powder in a small dish, then brush the mixture over the skewers.
Heat a grill pan or outdoor grill to medium-high heat and cook the skewers for 10-12 minutes, turning every few minutes until the meat is cooked through and slightly charred.
Serve the hot skewers immediately alongside the roasted potatoes.