In a large baking sheet, combine the tomatoes, chopped fennel, chopped onion, and garlic.
Drizzle 2 tablespoons of olive oil over the vegetables, and season with salt and black pepper to taste. Toss to coat the vegetables evenly.
Roast the vegetables in the preheated oven for about 30-35 minutes or until they become soft and start to caramelize, stirring once or twice during roasting.
Remove from the oven and place the roasted vegetables in a pot and add the stock.
Bring the mixture to a boil, then reduce the heat to low, cover and let it simmer for about 10 minutes to allow the flavors to meld together.
Use an immersion blender to puree the soup until smooth. Alternatively, you can carefully transfer the soup in batches to a blender and blend until smooth, then return it to the pot.
Season the soup with additional salt and black pepper to taste and heat it through.