In the meantime, cook the broccoli. Bring 3/4 cup / 180 ml water to a boil in a large pot. Add a big pinch of salt and stir in the broccoli. Cover and cook for 1 minute, just long enough to take off the raw edge. Quickly drain the broccoli in a strainer and run under cold water to stop the cooking. Drain well and set aside.
To make the pesto, combine 2 cups / 7 oz / 200 g of the cooked broccoli, the garlic, most of the pine nuts, the Parmesan, 1/4 teaspoon salt, and 2 tablespoons of the lemon juice in a food processor. Drizzle in the olive oil and creme fraeche and pulse until smooth.
Just before serving, toss the orzo and remaining cooked broccoli florets with about two-thirds of the broccoli pesto and the lemon zest. Thin with a bit of warm water if you like, then taste and adjust if needed. You might want to add a bit more salt, or an added drizzle of lemon juice, or more pesto. Gently fold in the avocado. Turn out into a bowl or onto a platter and top with the remaining pine nuts.