Roast the tomatoes. Preheat the oven to 400°F. Toss the tomatoes with the olive oil, salt, and pepper. Arrange on a baking sheet and roast for 40-50 minutes until soft and beginning to brown.
Meanwhile, make the marinara sauce. Heat the olive oil in a large pot over medium heat. Add the onion and sauté for 5 minutes, until beginning to soften. Add the garlic and cook 30 seconds. Add the tomatoes, oregano, salt and pepper. Bring to a boil then reduce heat and simmer partially covered for 15 minutes. Turn off the heat and stir in the fresh parsley or basil.
Cook the pasta according to the package directions. Drain and rinse well. Then return the pasta to the pot.
Pour the marinara sauce into the pot with the pasta and toss well. Gently stir in the roasted tomatoes and mozzarella slices.
Serve with a garnish of fresh basil and a sprinkle of black pepper.