Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Slice the Roma tomatoes in half and place them on the baking sheet along with the diced yellow onion and smashed garlic cloves.
Drizzle the vegetables with 0.5 tablespoon of olive oil and sprinkle with half of the sea salt, black pepper, and dried oregano.
Roast the vegetables for 25 to 30 minutes until the tomatoes are blistered and slightly charred around the edges.
While the vegetables roast, season the chicken breast with the remaining salt, pepper, and oregano, then grill in a pan with the remaining 0.5 tablespoon of olive oil over medium heat until the internal temperature reaches 165°F.
Transfer the roasted tomatoes, onions, and garlic into a high-speed blender, ensuring you include any juices from the pan.
Add the rinsed cannellini beans, vegetable broth, and fresh basil to the blender.
Blend on high speed for 60 seconds until the soup is completely smooth and velvety in texture.
Slice the grilled chicken breast into thin strips.
Pour the hot soup into a bowl and top with the sliced chicken breast and an extra leaf of fresh basil if desired.