Marinade: Whisk vinegar, oil, garlic, and oregano. Reserve 2 tbsp of the mixture.
Soak: Pour the rest over the chicken and marinate for 30 mins to 2 hours.
Grill: Preheat grill to medium-high. Grill chicken for 6-7 mins per side until internal temp hits 165°F.
Tomatoes: In the last 3 mins, place halved tomatoes on a foil sheet on the grill with the reserved marinade until soft.
Assemble: Top grilled chicken with the blistered tomatoes and a generous sprinkle of fresh basil.
Serve: Rest for 5 mins before slicing.