Preheat the oven to 350?.
Cut the tomato and onion into wedges. Use your fingers to scoop out some of the biggest pockets of seeds. Spread the tomatoes and onion on a rimmed baking sheet. Drizzle with olive oil and sprinkle with ½ teaspoon salt, a generous amount of pepper, and parsley. Gently toss with your hands to combine. Tuck the garlic cloves in the nook of the tomato so they won’t burn in the oven. Roast until the tomatoes have broken down and reduced to about half their original size, 30 to 40 minutes. Remove from the oven and let cool slightly.
In a large pot over medium heat, warm the broth and stir in the tomato paste to dissolve. Ad all the ingredients from the baking sheet to the broth and simmer gently for 5 minutes. Using an immersion blender, food processor, of blender, puree the soup until it is smooth but still has some texture. If you prefer a silkier soup, pass it through a fine-mesh sieve. Return soup to the pot, turn the heat to low, and stir in the cream. Add more salt and pepper to taste.
If you’re serving the soup with the cheesy toast, drizzle each slice of bread with a bit of olive oil and a slice of mozzarella cheese. Toast them in a toaster oven or under a broiler until the cheese is melted, about 5 minutes. Float a toast in each bowl of soup. Garnish with the oregano and serve hot.