Boil a large pot of salted water for the capellini. Keep in mind it only takes a few minutes to cook, so watch it carefully. I'd suggest not cooking the pasta until you're almost ready to serve.
Prepare the tarragon, lemon, parmesan cheese, and parsley (optional).
Wash scallops and trim the side muscle off them if need be (most grocery store scallops come with this already removed). Pat the scallops dry with paper towel (do this thoroughly). Sprinkle scallops with salt and pepper.