Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper.
Dice the chicken breast, sweet potato, and red bell pepper into bite-sized pieces, and halve the Brussels sprouts.
Place the chicken and vegetables on the sheet pan, drizzle with half of the olive oil, and season with sea salt, black pepper, and garlic powder.
Toss everything to coat evenly and roast for 20-25 minutes until the chicken is cooked through and the vegetables are tender and slightly browned.
While the pan roasts, whisk together the remaining olive oil, lemon juice, and Dijon mustard in a small bowl to create the vinaigrette.
Place the baby kale in a meal prep container or bowl, top with the roasted chicken and vegetable mixture, and add the sliced avocado.
Drizzle with the lemon vinaigrette just before serving or store the dressing on the side for later.