Combine the mint, parsley, basil, rosemary, oregano, garlic, lemon zest, lemon juice, salt, pepper and olive oil. Rub well into both sides of lamb. Place lamb in large zip-type storage bag or leave in bowl covered. Place into refrigerator for at least 2 days and up to 3.
Remove from refrigerator 1 hour before cooking to allow lamb to come to room temperature. Wipe off most herb mixture, reserving marinade for basting.
Roast lamb over coals or low gas grill heat covered for 20 minutes, basting and turning after 10 minutes. Remove cover and baste and grill another 10 minutes (5 minutes each side) or until lamb is cooked medium - medium rare. Remove to platter, tent with foil and let lamb rest for at least 15 minutes.
Slice thinly across the grain. Place in pita bread warmed quickly on the grill. Top with tzatziki sauce - recipe follows), shredded lettuce, chopped tomatoes, sliced red onion and crumbled feta cheese.
Tzatziki Sauce: Place yogurt into fine strainer lined with cheesecloth (or damp coffee filter). Set strainer over bowl and cover with plastic wrap. Let drain overnight to make "yogurt cheese". Discard whey mixture that accumulates in bottom of bowl.
Remove seeds from cucumber and grate. Salt lightly and let sit one hour. Squeeze grated cucumber to remove excess water. Mix cucumber with rest of ingredients into yogurt and let rest in refrigerator for at least 2 hours. Drizzle over gyros or serve in hollowed out red cabbage to make a clever presentation!
Cook's Notes: Allow 2-3 days for marinating the lamb and 1 day ahead to prepare the Tzatziki Sauce. The flavor of fresh herbs in this dish is incomparable, but dried herbs can be substituted if in a pinch, just reduce the quantity by half.