To prepare the pesto, combine the garlic scapes, mint, basil, arugula, salt and pine nuts in a food processor. Pulse until the ingredients are all chopped and then scrape down the sides of the bowl. With the machine running, add the olive oil until the ingredients are combined.
Bring a large pot of salted water to a boil. Cook to pasta according to package instructions.
While the pasta is cooking, add the avocado, 3 tablespoons pesto, milk, lemon juice, salt and pepper to a blender. Puree until smooth.
Drain the pasta, reserving about 1/4 cup of pasta water. Toss the cooked pasta together with the avocado pesto sauce. If the sauce is too thick, add the reserved pasta water, 1 tablespoon at a time, until the desired consistency is reached.
The garlic scape pesto recipe yields approximately 1 cup (enough to prepare this pasta dish 5 times). Pesto can be frozen in 3 tablespoon portions and then thawed for a quick and easy dinner.