In a small pan, heat 1/2 cup olive oil over medium heat. Add the lightly crushed garlic cloves and sauté until they turn light brown and fragrant, about 1–2 minutes; avoid burning. Remove and discard the browned garlic.
To the still-warm oil, add 1 tablespoon red pepper flakes and sauté for 1 minute, then turn off the heat and set the flavored oil aside.
Heat a large skillet over medium-high heat and add 1 tablespoon olive oil. Add the chicken sausage (removed from casings) and break it up with a wooden spoon; brown the sausage all over, about 5–7 minutes.
Add the sliced red and orange bell peppers to the skillet with the sausage and sauté until the peppers are soft, about 5–6 minutes.
Meanwhile, bring a large pot of salted water to a boil and cook 1 pound fettuccine until al dente according to package directions. Reserve about 1/2 cup of the pasta cooking water, then drain the pasta.
Add the drained pasta to the skillet with the sausage and peppers and toss to combine. Carefully pour in the reserved garlic–red pepper oil and add a splash of the reserved pasta water as needed to loosen the sauce.
Stir in 1/2 cup grated Parmesan and toss until the cheese melts and coats the pasta, adding more pasta water if needed for a silky sauce.
Remove the skillet from the heat and stir in the chopped parsley and basil. Taste and adjust seasoning as desired, then serve hot with additional Parmesan if desired.
