Prepare your skewer components: Wash and cut your zucchini into ¾ inch thick rounds. In a saucepan, steam potatoes and zucchini until tender.
Toss Zucchini in olive oil, salt and pepper. Once the potatoes are cool, lightly smash them using the palm of your hand and season with thyme, salt and pepper. Wash tomatoes and also season with olive oil, salt and pepper. Store the tomatoes, potatoes and zucchini in separate containers in the refrigerator.
Marinate the lamb: put the lamb into a large resealable plastic bag and add olive oil, garlic, and rosemary. Seal the bag and using your hands, make sure the marinade coats all of the lamb pieces. Let the meat marinate overnight in the refrigerator (or for at least 4 hours).
Heat your grill pan to medium/high heat.
Meanwhile, assemble your skewers: Put a skewer through the centre of a potato, followed by a tomato and a zucchini. Repeat until all of the vegetables are used up.
Grill each skewer for about 3 minutes on each side or until nice grill marks form.
Next, grill the lamb for about 2–3 minutes per side (lamb should be served medium, with a pink centre). Finish with a sprinkle of salt and pepper.
Serve lamb hot with vegetable skewers and a freshly tossed green salad. Squeeze some lemon on the lamb just before eating.