In a 12" cast-iron skillet over medium high heat, add 2 Tbsp. of olive oil. Season both sides of chicken breasts evenly with ¼ tsp. pepper. Add chicken to skillet and sear until golden on both sides, about 5 min. per side. Transfer to a plate to let rest.
Add remaining olive oil to skillet. Add chopped onion and garlic, season with remaining pepper and cook until onion starts to become translucent and garlic is fragrant, about 2 min. Add cherry tomatoes and corn, stir to coat in onion-garlic mixture. Lower heat to medium; cover and let cook for about 15 min. until tomatoes burst open.
Meanwhile, slice chicken breasts on a diagonal.
Remove lid from skillet; top tomato and corn mixture with sliced chicken and cubed VELVEETA. Cover to let VELVEETA melt and chicken warm, about 10 min. Remove lid. Garnish with fresh basil and serve.