Preheat the oven to 220℃/428℉.
Arrange potato, sweet potato and carrots on baking paper in a baking tray. Cover all with a drizzle of olive oil. Sweet potato and carrots can be dusted with a little cumin. Salt and pepper for the potatoes.
Bake for 20 minutes before turning and adding the broccolini. Drizzle broccolini with olive oil.
At 30 minutes the vegetables should be nearly done. Potatoes will be browned and carrots caramelising. Sweet potato will be soft. All vegetables should easily be pierced with a knife. If not, allow for longer time. Turn to ensure they don't stick to the paper and the broccolini tips don't over-brown. I often like to change the baking paper if it's a bit too oily here. This also helps crisp up the potato. Bake for another 10 minutes. Meantime, coat the fish with a little flour mixed with salt and pepper. If going gluten-free, just season. The flour helps protect the fish from over-cooking. Warm a small amount of olive oil in pan on medium-high heat and add the butter. Add capers. Fry fish 2-3 minutes each side until lightly browned and easily flaked.
Season with salt, pepper, lemon and herbs. Serve with a little of the caper-butter sauce from the pan.