Using tongs, place the bell peppers over a gas flame. Cook, turning occasionally, until the skins are charred on all sides, about 5 to 6 minutes. (Alternatively, place the peppers on a baking sheet and broil for 5 to 8 minutes, until charred.) Place the charred peppers in a medium bowl. Cover the bowl with plastic wrap and allow the peppers to steam for 20 minutes. Under running water, peel away the charred skin from the peppers. Pat the peppers dry with paper towels. Remove the stem and seeds from the peppers and cut into 1/4-inch thick slices. Set aside.
In a medium saucepan, bring the chicken stock, water, and kosher salt to a boil over high heat. Add the pasta and cook until tender but still firm to the bite, stirring occasionally, about 8 to 10 minutes.
While the pasta is cooking: In a large skillet, heat the oil over medium-high heat. Add the turkey sausage and saute until cooked through, about 4 minutes. Add the garlic and cook for 1 minute. Add the bell peppers, tomatoes, and red pepper flakes, if using, and cook until heated through, about 2 minutes.
Drain the pasta, reserving about 1/2 cup of the cooking liquid, and transfer to a large serving bowl. Add the sausage mixture, 1 tablespoon of the parsley, and season with salt and pepper, to taste. Toss well to combine all ingredients, adding reserved cooking liquid, if needed, to loosen the pasta. Top with the ricotta salata and sprinkle with the remaining parsley. Serve.
Recipe courtesy of Giada De Laurentiis, 2008