Heat a small pan over medium heat. Add almonds and toast, about 2 minutes. Let cool slightly and roughly chop.
Bring a large pot of lightly salted water to a boil. Cook spaghetti in the boiling water, stirring occasionally, until tender yet firm to the bite, about 12 minutes.
While pasta cooks, add olive oil to a saucepan over medium heat. Add zucchini, garlic, salt, and pepper and fry until tender, 3 to 5 minutes.
Reserve 1/4 cup of the pasta cooking water and drain. Add cooked spaghetti to the saucepan with the zucchini. Add butter, parsley, lemon zest, lemon juice, and toasted almonds and stir to coat.