Cut off the top third of each squash, and then use a melon baller to scoop out the inside pulp- leaving a 1" thick shell behind. Discard the pulp.
Bring a large stock pot full of water to a rolling boil, and boil the prepared squash for 5 minutes, or just until barely fork tender. Using tongs remove them from the hot water, and set them aside to drain.
Add both the meats to a large skillet set over medium heat, and using a meat chopper cook breaking the meat up as it browns.
When the meat's halfway done, stir in the onion & garlic, and continue to cook until the meat's browned throughout.
Strain off most of the fat, and then return the skillet to the stove over low heat. Stir in the spinach.
Cover and let the mixture cook for 2 minutes, or just until the spinach has wilted. Uncover the skillet, and cook off almost all remaining liquid, stirring as it cooks.
Remove the skillet from heat, and let the meat mixture cool for 15-20 minutes.
Make sure the mixture's cool, then stir in the beaten egg, pepper, half of the dill, orzo pasta, and half the feta until everything's evenly incorporated.
Add the prepared squash to a baking tray, and spoon the filling evenly into the cavities. Sprinkle the remaining feta cheese evenly out overtop of the stuffed squash.
Bake the prepared squash at 350° for 25-30 minutes, or until the stuffing is golden brown on top and the squash is tender.
Sprinkle the rest of the dill evenly out over the baked squash, and serve.