Before you start, preheat oven to 220°C (or 200°C fan bake). Preheat two oven trays.
Prep kūmara, spread in a single layer on a lined oven tray and toss with oil. Season with salt and pepper and roast for 12-15 minutes, until just tender. Turn once during cooking.
In a small bowl, combine pesto and yoghurt.
In a medium bowl, toss rocket with olive oil and vinegar. Season taste with salt and pepper.
Prep capsicum and cheese. Combine tomato paste and tomato sauce together, divide mix between pizza bases and spread evenly. Top with cooked kūmara, capsicum and cheese. Season with salt and pepper.
Transfer 2 pizzas to each preheated tray and cook for 12-14 minutes, until bases are crisp and golden around the edges. Swap trays halfway through cook time to ensure even cooking.
Pat lamb dry and season with salt and pepper. Heat oil in a large fry-pan on medium-high heat. Cook lamb for 4-5 minutes each side for medium (depending on thickness), or until cooked to your liking. Rest, covered.
Thinly slice lamb and evenly distribute on pizzas. Top with half the rocket and dollop over yoghurt. Cut pizza into slices.
Serve pizza with remaining rocket on the side.