Season chicken breasts with Kosher salt and freshly ground black pepper.
Heat a heavy-bottomed sauté pan over medium-high. Add olive oil and heat for another minute. Add chicken to pan and cook 2 to 3 minutes on each side until the breasts are lightly browned. Remove chicken from skillet and set aside.
Add some butter to the pan and heat until it foams. Then add the onions and cook until translucent, about 2 minutes. Add wine and bring mixture to a boil. Return the chicken to the pan and add the tomato wedges. Cover and reduce heat. Simmer 10 minutes or until chicken is tender and cooked through.
Remove chicken and plate it. Add the chopped olives and thyme to the pan and cook for another minute, then top the chicken with the sauce and serve immediately.