With lamb we find it best to stay away from Oaky reds. In general new world wines (Australia and New Zealand) will be fruitier than their European equivalents and so often will be a better option. A Syrah will rarely disappoint when combined with a lamb based dish.
If you are only able to buy North American wine, then avoid anything too sweet, even if you usually like a sweeter wine.
A good bordeaux is actually my favorite option, but speak to the shop owner to ensure it isn’t oaky (now that is why you should buy your wines somewhere other than the local supermarket).
The rest of the world seems to favor a spanish Rioja with lamb.
A good rioja can work well if the dish is particularly robust or has Mediterranean notes, for example, a Moroccan lamb tajine. If for some reason you cannot find a Rioja on the day, a Tempranillo will do just as well.
Saving my special recoomendation till the end I would say you should go get a bottle of Cabernet Sauvignon from 2003. The vintage year produced amazing Cabernet Sauvignon and since few lamb dishes can get overwhelmed, a bottle of Cabernet Sauvignon on the table is going to make everybody happy. By following your taste buds I am sure you will find the wine with lamb dishes that suits you best.