Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper for easy cleanup.
Dice the chicken breast, sweet potato, zucchini, and red bell pepper into uniform 1-inch pieces to ensure even roasting.
In a small mixing bowl, whisk together the olive oil, lemon juice, minced garlic, dried oregano, sea salt, and black pepper until well combined.
Place the chicken and all the chopped vegetables into a large bowl, pour the lemon-herb dressing over them, and toss until every piece is thoroughly coated.
Spread the mixture in a single, even layer across the prepared baking sheet, making sure not to overcrowd the pan so the vegetables can crisp up.
Roast in the center of the oven for 20 to 25 minutes, tossing halfway through, until the chicken is cooked through and the sweet potatoes are fork-tender.