Preheat an electric smoker to 250°F. Add wood chips according to the smoker’s instructions.
In a large bowl, whisk the egg and milk. Stir in the breadcrumbs and let them soften for a minute.
Add the ground beef, feta, olives, sun-dried tomatoes, red onion, garlic, oregano, salt, and black pepper. Mix gently with your hands just until combined. Avoid compacting the mixture, which can make the meatloaf dense.
Lightly coat a small loaf pan with the olive oil. Shape the meat mixture into a loaf and place it in the pan. If your smoker has a rack designed for meatloaf, you can shape the loaf on that instead.
Smoke the meatloaf at 250°F until the center reaches 160°F on an instant-read thermometer, about 2 to 2½ hours. Check the temperature in the thickest part of the loaf.
Carefully remove the meatloaf from the smoker and let it rest for 10 minutes before slicing. This helps it hold together and keeps the slices tender.