Add a splash of oil to a large pot of boiling salted water and cook the spaghetti al dente. Drain the pasta in a colander, place it in a large bowl, and while still warm, toss with 3/4 of the sauce. Add the red and yellow peppers and spring onions; toss well. Serve warm or at room temperature. The remaining sauce may be added, as needed, to moisten the pasta.