Preheat the oven to 425 degrees F.
Slice the cauliflower and break it into pieces. On a sheet pan, toss the cauliflower with olive oil, salt and pepper. Spread it into a single layer.
Stir the pesto into the pasta. Then fold in the roasted cauliflower and chives.
Divide the pasta into bowls and top with chopped pistachios and shaved parmesan before serving.