Cook the pasta according to the package directions.
If you wish to toast the pine nuts, place them in a small skillet over medium-low heat.
Toast until they turn a light golden color, then remove from heat.
Meanwhile, heat a large skillet over medium heat and add 2 tablespoons of butter, the diced zucchini, and salt.
Sauté for 3 to 4 minutes, until the zucchini becomes tender.
Add the remaining 1 tablespoon of butter and the minced garlic to the skillet.
Sauté for an additional minute.
Stir in the lemon juice, lemon zest, red pepper flakes, and black pepper, mixing well.
Add the cooked pasta to the skillet and toss everything together until combined.
Sprinkle with parmesan cheese and the toasted pine nuts, if using.
Divide into bowls and serve.