Roast the tomatoes. Preheat an oven to 425°F (218°C). Place (300g) tomatoes on a rimmed baking sheet, drizzle with 2 Tbsp olive oil, then season with ½ tsp kosher salt. Cook for 20-25 minutes, rotating the pan once halfway through, until the tomatoes have shriveled and blistered a bit. Set aside.
Cook the pasta. Meanwhile, bring a large pot of water to a rapid boil, then season generously with a few tablespoons of kosher salt. Add 1lb (454g) pasta, then cook according to package directions until al dente (or 1 minute more, depending on your preference). Reserve about ½ cup of pasta water, then drain. Transfer the pasta to a large mixing bowl.
Cook the shrimp. Place shrimp in a mixing bowl, then season with 1 tsp Italian seasoning, 1 tsp kosher salt, and ¼ tsp black pepper. Toss well. Heat remaining 2 Tbsp olive oil in a large skillet over medium-high heat. Add shrimp, ensuring they’re in a single layer, then cook undisturbed for 2 minutes. Flip the shrimp, then cook for 1-2 minutes more, or until the shrimp turn opaque and are cooked through.
Add remaining ingredients. Add cooked tomatoes, pan-seared shrimp, ½ cup pesto, ½ cup mascarpone cheese, halved bocconcini, lemon zest, and ¼ cup reserved cooking water, then toss to combine until the sauce is well mixed. Taste and adjust seasoning as needed. For a thinner sauce, add reserved pasta water a tablespoon at a time, tossing well in between, until desired consistency is reached.
Finish, then serve! Transfer to a serving bowl. If you want the pasta salad chilled, cover tightly, refrigerate for at least 2 hours, then garnish as follows. If serving warm, drizzle with a little extra virgin olive oil, sprinkle with a pinch of flaky sea salt and black pepper, then garnish with fresh basil leaves. Enjoy!