Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Dice the chicken breast, eggplant, zucchini, red bell pepper, and yellow onion into uniform 1-inch cubes to ensure even cooking.
Place the chicken and chopped vegetables onto the baking sheet and drizzle with olive oil.
Season the mixture with dried oregano, sea salt, and black pepper, then toss thoroughly to coat every piece.
Spread the ingredients into a single layer and roast for 20 minutes until the chicken is cooked through and the vegetables are tender.
Remove the pan from the oven and pour the tomato puree over the roasted mixture, adding the minced garlic.
Toss gently to combine and return the pan to the oven for an additional 5-7 minutes until the sauce is bubbling.
Garnish the ratatouille with fresh torn basil leaves before serving warm.