Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper.
Dice the sweet potato into half-inch cubes, slice the carrots into rounds, and break the broccoli into bite-sized florets.
Toss the prepared vegetables on the baking sheet with 1 teaspoon of olive oil, half of the sea salt, and half of the black pepper.
Roast the vegetables for 20 to 25 minutes, tossing halfway through, until the sweet potatoes are tender and the broccoli edges are slightly charred.
While the vegetables roast, season the chicken breast on both sides with the dried oregano and the remaining salt and pepper.
Heat the remaining teaspoon of olive oil in a medium skillet over medium-high heat and sear the chicken for 6 to 7 minutes per side until golden and cooked through.
In a small bowl, whisk together the Greek yogurt, lemon juice, and minced garlic until smooth.
Reduce the skillet heat to low, add the yogurt mixture to the pan with the chicken, and stir constantly for 1 minute to create a creamy coating without curdling.
Plate the creamy chicken alongside the roasted vegetable medley and serve immediately while hot.