Preheat oven to 220°C. Drizzle some EVOO into a baking dish and set aside.
Pour 1 litre of water into the Thermomix bowl. Line the Varoma dish with paper and place lamb into the Varoma and season with salt and pepper all over. Steam 25 min/Varoma/speed 4. Drain Thermomix bowl of water.
Place the steamed lamb into the prepared baking dish and bake for 30 minutes (depending on the size of lamb).
Meanwhile make the pesto by placing peppercorns, lemon zest, garlic and herbs into the Thermomix bowl and mill 8 sec/speed 8.
Add remaining ingredients except oil and blend a further 5 sec/speed 8. Scrape down with spatula if necessary.
With blades rotating on speed 3, add enough EVOO through lid to just bring the mix to a solid paste.
Take the lamb out of the oven and coat with the pesto. Return to the oven for a further 10 minutes, until crust is fragrant and golden. Keep your eye on it so the pesto doesn't burn. Rest for at least 20 minutes, covered, before serving.
To flash roast the tomatoes, place them in a baking dish, lined with baking paper, drizzle with EVOO, balsamic vinegar, salt and pepper. Place in a hot oven for 7 minutes or until starting to blister.
Serve lamb on a bed of rocket, with a garnish of mint and rosemary. Roasted tomatoes and potatoes on the side.