Grilled Chicken and Vegetable Mozzarella Melts - Ellie Krieger

Ingredients

• 5 tablespoons olive oil, divided, or more if grilling the entire vegetables
• 1 1/2 tablespoons white wine vinegar
• 1 teaspoon dried oregano
• 3/4 teaspoon kosher salt, divided, or more as needed
• 1/2 teaspoon freshly ground black pepper, divided, or more as needed
• 2 cloves garlic, coarsely chopped
• 4 skinless boneless chicken breasts (about 6 ounces each) pounded to 1/2-inch thick
• 1 small globe eggplant (about 1 pound), trimmed
• 1 medium red bell pepper, stemmed and seeded
• 1 medium sweet onion, such as Vidalia
• 1/4 cup prepared marinara sauce, at room temperature
• 2 ounces fresh mozzarella, very thinly sliced
• 4 fresh basil leaves, or more to taste