Bring a large pot of generously salted water to a boil and cook the fettuccine, stirring occasionally, until al dente, about 6 minutes. (While pasta is cooking, scoop out 1-1/2 cups of pasta cooking water.)
Meanwhile, melt the butter in a 10-inch straight-sided sauté pan over medium heat. Add the garlic and cook until softened and fragrant, but not browned, about 1 minute. Add 1 cup of of reserved pasta water. Add the sliced vegetables and peas or lima beans (if using fresh). Cover and simmer until the vegetables are just tender, about 3 minutes. Add the cream and lemon zest along with any fava beans or thawed, frozen peas or lima beans (if using). Bring to a simmer.
Drain the fettuccine and return to its cooking pot. Toss with the vegetables and cream sauce, pea shoots (or watercress or arugula), Parmigiano, all but 1 Tbs. of the herbs, and the pepper flakes. Season to taste with salt and pepper. If necessary, adjust the consistency of the sauce with the reserved 1/2 cup pasta water; the sauce should generously coat the vegetables and pasta. Serve immediately, sprinkled with the remaining fresh herbs and the pine nuts.