Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Trim the ends of the Brussels sprouts and cut them in half lengthwise.
Toss the sprouts on the baking sheet with 0.5 tablespoons of avocado oil, half of the sea salt, and half of the black pepper.
Spread the sprouts in a single layer and roast for 20 to 25 minutes, tossing once halfway through, until the outer leaves are dark and crispy.
While the sprouts roast, season the chicken breast on both sides with garlic powder and the remaining salt and pepper.
Heat the remaining avocado oil in a non-stick skillet over medium-high heat and sear the chicken for 6 to 7 minutes per side until cooked through.
In a small saucepan over low heat, whisk the balsamic vinegar and honey together, simmering for about 4 minutes until it thickens into a syrup-like glaze.
Remove the chicken from the pan and let it rest for 3 minutes before slicing.
Plate the chicken and roasted Brussels sprouts, then drizzle the warm balsamic glaze over both before serving.