Bring 6 quarts water to a boil in a large pot. Add the pasta; cook according to package instructions until al dente.
Meanwhile, heat oil, red-pepper flakes, and garlic in a medium saucepan over medium heat, stirring occasionally, until oil is hot but not smoking, about 2 minutes. Add bell-pepper strips, and cook until very soft, about 20 minutes.
Drain pasta well. Rinse with warm water; shake out excess. Return pasta to pot. Stir salt into bell-pepper mixture; add to pasta, and toss well to coat.