Preheat the oven to 180C. Chop the tomatoes into wedges. Remove the stem end.
In a large bowl, add the olive oil, garlic, dried oregano and onion. Mix them together.
Add the tomatoes to the oil mixture. Toss the tomatoes to coat. Place everything on a tray. Roast them in the oven for an hour or so.
When it's done, use tongs to try and remove the skin from the tomatoes.
Add everything in a pot with chicken stock and put on medium heat.
Add the tomato paste to the soup. Season with salt and black pepper.
Add the basil leaves.
Use a hand blender and blitz everything together. Or pour the mixture into a blender jug and pulse first. When it looks like it's not spitting anymore, blitz away. Remember to keep the lid on!
Serve sprinkled with some cheese on top and baguette slices.