Preheat the oven to 160ºC fan.
Thinly slice the baby potatoes and add to a large deep baking tray.
Drizzle over 1-2 tbs olive oil and roast in the oven for 10 minutes.
Halve the carrots length-ways and add to the tray with the asparagus and stir.
Place the whole sea bream on top of the vegetables, add a few lemon slices to the cavities of each fish, and the rest in amongst the vegetables.
Drizzle everything with a little more olive oil and season with salt and pepper.
Scatter over most of the thyme then return to the oven for 20-25 minutes or until the fish is cooked and the vegetables are tender and golden.
Serve the traybake straight to the table or divide between two plates, drizzle with a little extra olive oil and sprinkle with some fresh thyme leaves.
