Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Halve the brussels sprouts, chop the bell pepper into bite-sized pieces, and cut the red onion into thin wedges.
Toss the vegetables on the baking sheet with half of the olive oil, half of the sea salt, half of the black pepper, and all of the dried oregano.
Roast the vegetables for 20 to 25 minutes, tossing halfway through, until they are tender and the edges are slightly charred.
While the vegetables roast, season the chicken breast with the remaining salt and pepper.
Heat the remaining olive oil in a medium skillet over medium-high heat and sear the chicken for 5 to 7 minutes per side until fully cooked through.
In a small jar, whisk together the balsamic vinegar, honey, and minced garlic.
Reduce the skillet heat to low, pour the balsamic mixture over the chicken, and simmer for 2 minutes until the sauce thickens into a glossy glaze.
Slice the chicken and serve immediately alongside the roasted vegetable medley.