Put the garlic, pine nuts, serrano and some salt in a mortar and pestle and mash to a chunky, pesto-like consistency. Add the cilantro and continue to mash; the pesto should be very coarse.
Put the avocados and lime juice in a bowl and sprinkle with salt and pepper. Gently fold in the pesto until just combined, being careful not to mash the avocado too much.
Recipe courtesy of Bobby Flay