Preheat your oven to 400°F (200°C) and line a 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 half of the olive oil and sprinkle with half of the sea salt and black pepper.
Roast the vegetables for 25 to 30 minutes until they are soft and the tomato skins are slightly charred.
While the vegetables roast, season the chicken breast with the dried oregano and the remaining sea salt and black pepper.
Heat the remaining olive oil in a skillet over medium-high heat and sear the chicken for about 6 minutes per side until fully cooked.
Transfer the roasted tomatoes, onion, and garlic into a high-speed blender, ensuring you include any juices from the pan.
Add the chicken broth, fresh basil, and Greek yogurt to the blender and process until the soup is completely smooth and creamy.
Slice the cooked chicken breast into thin strips.
Pour the warm soup into a bowl and top with the grilled chicken strips to serve.