I flavour my own olive oil by adding crushed garlic, fresh thyme and rosemary. Apart from cooking with it, it's great on salads or making a salad dressing. On occasions I also add grated ginger and shredded chillis. You can really add what you want and it's interesting to experiment with flavours. Go for it.
Almost forgot. What should you do with it?? The roast lamb sounds great. Try quickly shallow frying some calves liver, sliced pork fillet or, almost anything. Don't be afraid to try things out.
Try pouring it over a selection of peeled & chunked veggies ( courgette,sweet potato, aubergine- anything really) then roast them in a hot oven. Good as a side dish with the roast lamb.