Preheat your oven to 400°F (200°C).
Halve the Roma tomatoes and place them on a baking sheet with the chopped onion and garlic cloves.
Drizzle the vegetables with olive oil and roast for 25-30 minutes until the tomatoes are soft and slightly charred.
While vegetables roast, poach or pan-sear the chicken breast until it reaches an internal temperature of 165°F, then shred it into small pieces.
Transfer the roasted tomatoes, onion, and garlic into a high-speed blender, adding any juices from the pan.
Add the chicken broth and fresh basil to the blender and process until the mixture is completely smooth.
Pour the soup into a medium pot over low heat.
Stir in the shredded chicken and Greek yogurt, whisking gently until the soup is creamy and heated through.
Season with sea salt and black pepper, then serve warm.