Bring a pot of water to boil, then add zucchini for one minute. Drain the zucchini and rinse with cold water. Drain well again.
In a medium saucepan, melt the butter over low heat on the stove. When butter has melted, whisk in flour for one minute. Slowly pour in milk while whisking until there aren’t any lumps of flour. Mix in minced garlic and crushed red pepper.
Begin adding feta to the mix, a little at a time, while whisking. Once the sauce is smooth, mix in basil and lemon zest. Mix zucchini noodles in with the sauce before serving, or pour the sauce over, if you prefer.