Bring a large pot of heavily salted water to a boil. Add pasta and cook until al dente (1 minute less than package instructions). Drain pasta, reserving a cup of the hot pasta water.
If the tomatoes are different sizes (like the farmer’s market mixed heirlooms), cut the cherry-sized ones in half and leave any small ones whole, so they’re all roughly the same size.
Meanwhile, heat a large skillet over medium-high, add oil and give it a swirl to coat the bottom. Add the pancetta and cook until it starts to render and turn a little brown, about 2 minutes. Add garlic and red pepper flakes and cook until fragrant, about 2 minutes. Add the tomatoes and stir until they are coated in the oil. Season with a little sea salt and pepper, to taste. Cook until the tomatoes shrivel up slightly, release some juice and brown a bit at the edges, about 5 to 8 minutes.
Add the drained pasta to pan with the tomatoes and toss (if the mixture looks dry add a little pasta cooking water a few tablespoons at a time). Cook over high heat until the pasta finishes cooking in the sauce. Add the butter and toss until it melts and coats everything.
Turn off the heat and top with a generous mound of fresh basil and scallions. Drizzle with olive oil and sprinkle with sea salt and more pepper before serving.
Note: If you want to make the dish vegetarian, leave out the pancetta and toss 1/3 cup grated pecorino in with the butter.