Preheat oven to 425 degrees. Place tomatoes, red onion, and bell pepper, and garlic on a baking sheet. Drizzle with 2 tablespoons of olive oil and season with salt and pepper. Roast for 25 minutes or until tomatoes are soft and charred on the tops.
While the tomatoes are roasting, heat 1 tablespoon of olive oil in a medium-sized saucepan over medium-high heat. Add the diced potato. Cook until the potato begins to crisp, about 8 minutes, stirring occasionally. Stir in the tomato paste. Pour in the vegetable broth. Cover and bring to a boil.
Reduce the heat to low and simmer until the potato is fork-tender, about 15 minutes. Add the roasted tomatoes, red onion, bell pepper, and garlic to the broth. Blend the soup using a blender or immersion blender until smooth.