Soak panko in milk for 5 minutes. Stir in eggs, feta, olives, roasted peppers, onion, garlic, oregano, salt and black pepper.
Fold in beef and lamb just until combined. Shape a 9-by-5-inch loaf about 2 1/2 inches high on a parchment-lined metal tray.
Freeze before baking: freeze the raw shaped loaf promptly until firm, then wrap tightly, place in a freezer bag, label and freeze for up to 2 months. Keep oil, lemon juice and reheating broth separate.
Thaw the wrapped loaf on a rimmed tray in the refrigerator for 24 to 48 hours until fully thawed. Remove all wrapping and place on a parchment-lined rimmed baking sheet.
Heat the oven to 375°F. Mix oil and lemon juice and brush over the loaf, then bake for 60 to 70 minutes until the center reaches 160°F.
Rest for 10 minutes and cut into 8 slices. Refrigerate cooked leftovers within 2 hours.
Reheat cooked slices covered with a little reserved broth at 350°F for 20 to 25 minutes until the centers reach 165°F.