Bring a large pot of salted water to a boil for pasta.
In a large skillet, over medium-high heat, heat 4 tablespoons of olive oil.
When the oil is hot, add the garlic.
Once the garlic is sizzling, add the leeks and zucchini.
Cook until softened (about 4 minutes).
Season the vegetables with the salt and crushed red pepper.
Add the tomatoes and 4 ounces of pasta cooking water.
Bring to a simmer and cook until slightly thickened.
In the meantime, add the fettuccine noodles to the boiling water.
While the fettuccine is cooking, add the shrimp to the sauce and bring back to a boil.
Cook for another 5 minutes.
When the pasta is al dente, drain and add to the sauce.
Add the chopped basil and toss to coat the pasta with the sauce.
Remove the skillet from the heat.
Drizzle with the remaining 2 tablespoons oil.
Toss and serve hot.