I have a pretty small garden, with not even enough room for the number of roses I'd like to grow, so I appreciate multi-purpose plants, lavender fits this quite nicely. It can be used for more than toiletries though.
Next you'll need some lavender, you just want the flowers and since they are currently in bloom use fresh ones, you need a handful (if you have to use dried, they are more intense, so halve the amount), a couple of sprigs of rosemary and 4-5 garlic gloves. Grind it together with some pepper & salt and then add a dash of olive oil to bind it. Coat the lamb & leave it for a couple of hours.
The lavender is quite a delicate flavour, which comes as a bit of a shock after the grinding (which can make your kitchen smell like a natural trust gift shop) and really complements the lamb well.