Dice the chicken breast into 1-inch cubes and chop the sweet potato, zucchini, bell pepper, and red onion into uniform bite-sized pieces.
Heat the olive oil in a large cast-iron skillet over medium-high heat until shimmering.
Add the diced sweet potatoes to the skillet and cook for 5 to 7 minutes, stirring occasionally, until they begin to soften and develop a golden-brown crust.
Push the potatoes to the outer edges of the skillet and add the chicken cubes to the center.
Season the chicken with half of the sea salt, black pepper, and dried oregano, cooking for 4 minutes until the edges are opaque and browned.
Add the red onion, bell pepper, zucchini, and minced garlic to the skillet, stirring everything together to combine.
Sauté the mixture for an additional 5 to 6 minutes until the vegetables are tender-crisp and the chicken is fully cooked through.
Sprinkle with the remaining salt, pepper, and oregano before serving hot directly from the skillet.