1. Preheat your oven to 400 F (200 C). Line a large baking sheet with parchment paper for easy cleanup.

2. On the prepared baking sheet, scatter the cherry or grape tomatoes and red onion wedges. Drizzle with 1 tablespoon of olive oil, a pinch of salt, and pepper. Toss gently to coat.

3. Pat the chicken breasts or thighs dry with paper towels. Place the chicken pieces among the vegetables on the baking sheet, ensuring they are in a single layer and not overcrowded.

4. In a small bowl, whisk together the remaining 1 tablespoon of olive oil, balsamic vinegar, honey (or maple syrup), minced garlic, dried oregano, 1/2 teaspoon salt, and 1/4 teaspoon black pepper until well combined.

5. Pour about two-thirds of the balsamic mixture over the chicken and vegetables on the baking sheet. Use a brush or spoon to ensure everything is evenly coated. Reserve the remaining glaze for later.

6. Place the baking sheet in the preheated oven and roast for 15 minutes.

7. Remove the baking sheet from the oven. Drizzle the remaining balsamic glaze over the chicken and vegetables. Return to the oven and cook for another 5-10 minutes, or until the chicken is cooked through (internal temperature reaches 165 F / 74 C) and the sauce has thickened slightly and caramelized. The tomatoes should be tender and slightly blistered.

8. Once cooked, remove from the oven. Let it rest for a few minutes before serving. Garnish with fresh basil leaves, if desired.