How to Make It
In a small saucepan, cover the shrimp shells with the water. Add the sliced celery and carrot and boil the shrimp shells over high heat until the liquid has reduced to 1 cup, about 20 minutes. Strain the shrimp stock through a fine-mesh sieve into a small bowl, pressing hard on the solids with the back of a spoon to extract the liquid. Season the shrimp stock with salt.
In a large pot of boiling salted water, cook the fettuccine until just barely al dente. Drain the fettuccine, reserving 1/4 cup of the pasta cooking water.
In a large, deep skillet, heat 3 tablespoons of the olive oil until shimmering. Add the sliced zucchini and garlic and cook over high heat, stirring frequently, until the zucchini is just softened and beginning to brown, about 5 minutes. Add the shrimp stock, fettuccine, shrimp, tomato sauce, basil, oregano and the remaining 2 tablespoons of olive oil. Add a pinch of crushed pepper and simmer over moderate heat, tossing constantly, until the shrimp are pink and the sauce is nearly absorbed, about 4 minutes. Add the torn zucchini blossoms and toss just until they are wilted. Stir in the reserved pasta cooking water and season the fettuccine generously with salt and pepper. Transfer the fettuccine to a large serving bowl and serve immediately.