Bring a pot of generously salted water to a boil and drop in the spaghetti.
While the pasta is cooking combine the basil, zest, juice, cheese and oil. mix together until combined. Cook the spaghetti until al dente. Before draining scoop out a cup of the pasta water and reserve.
Drain the spaghetti and add to the mixing bowl. Toss together until all the ingredients are fully incorporated. If the mixture is dry add some of the pasta water to loosen.
Portion into bowls and sprinkle with toasted almonds.