Set a medium saucepan over medium-high heat. Add the pistachios in a single layer and cook for about 3 minutes, stirring frequently until lightly toasted. Transfer the nuts to a cutting board. Once cool enough to handle, roughly chop and set aside.

In the same saucepan, add water with a generous pinch of salt and bring to a boil. Add the couscous to the boiling water, reduce heat to low, and simmer for 10-12 minutes until the couscous is al dente. Drain any excess water using a fine mesh sieve.

Return the cooked couscous to the pot. Drizzle with olive oil and stir to coat. Add the lemon juice, salt, and black pepper. Gently stir in the toasted pistachios until evenly distributed.

Adjust seasoning to taste and serve warm or at room temperature.