While the pasta is cooking, combine the drained cashews, garlic, and broth in a high-speed blender or food processor. Process until smooth and well blended. Peel and pit the avocado and add it to the food processor along with the scallions, lemon juice, salt, and pepper to taste. Process until smooth and creamy. For a thinner sauce, add some almond milk, if needed. For a thicker sauce, add additional avocado. Taste and adjust the seasonings, if needed.