How to Make It
In a food processor, pulse three-fourths of the tomatoes with the chopped scallions and the 1/4 cup of olive oil to a coarse puree; season with salt and pepper.
Light a grill or preheat a grill pan. Drizzle the whole scallions with olive oil and season them with salt and pepper. Grill the scallions over high heat until lightly charred and tender, about 1 minute per side. Transfer the grilled scallions to a work surface and cut them into 1-inch pieces.
In a large pot of salted boiling water, cook the pasta until al dente. Drain and transfer to a large serving bowl. Add the tomato-scallion puree and the grilled scallions; toss well. Season with salt and pepper. Top the pasta with the remaining chopped tomatoes and serve.