Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Slice the Roma tomatoes and yellow onion into halves and place them on the baking sheet along with the peeled garlic cloves.
Drizzle the vegetables with olive oil and season evenly with sea salt and black pepper.
Roast the vegetables for 30 to 35 minutes until they are tender and the tomato skins are slightly charred.
Transfer the roasted tomatoes, onion, and garlic into a high-speed blender, ensuring you include any juices from the pan.
Add the vegetable broth, Greek yogurt, and fresh basil leaves to the blender and process until the soup is completely smooth and creamy.
While the soup is being prepared, grill the chicken breast in a lightly greased skillet over medium-high heat until it reaches an internal temperature of 165°F.
Slice the chicken into thin strips and serve it over the warm tomato soup, garnishing with extra basil if desired.