Marinate chicken: Pat chicken dry, and pound chicken to an even 1⁄2-inch thickness. In a bowl, combine BBQ spice, 2 teaspoons each olive oil and water, and a few grinds of black pepper. Add chicken to bowl, tossing gently to coat.
Prep ingredients: Peel and finely chop 1 large garlic clove. Shuck corn, then cut kernels from cobs, then thinly slice scallions. Pick basil leaves from stems and thinly slice leaves.
Season sour cream: In a small bowl, combine 2 tablespoon sour cream, 1 tablespoon of water and olive oil, and 1⁄4 teaspoon each cider vinegar, chopped garlic, and salt. Whisk until smooth. Season with black pepper.
Cook corn & tomatoes: Heat 1 tablespoon of olive oil in heavy skillet over medium-high. Add tomatoes; cook until brown, about 3–4 minutes, crushing gently with a spoon to release juices. Add corn, remaining chopped garlic, and 1 tablespoon olive oil. Cook, until corn is tender, about 3–4 minutes. Season with 1⁄4 teaspoon salt and pepper.
Cook chicken: Transfer corn and tomato mixture to a medium bowl. Add 1 tablespoon of olive oil to skillet over medium-high heat. Add chicken. Cook for 3–4 minutes per side, until golden-brown. Transfer chicken to plates.
Finish & serve: Into the corn-tomato sauté, add basil, 2 teaspoons of vinegar and olive oil and 2⁄3 of the scallions. Serve chicken topped with sour cream sauce alongside of the corn-tomato sauté. Garnish with remaining scallions.