Heat your oven to 200°C/Fan 180°C/Gas 6. Trim your courgettes, then chop them into chunks around 2cm across. Toss them in a bowl with 1 tbsp olive oil and a pinch of salt and pepper. Tip the courgette into a roasting tin. Roast on the top shelf of the oven for 15 mins.
While the courgettes roast, finely grate half the chunk of the Parmesan. Finely grate the zest off the lemon. Set the zested lemon aside. Finely chop the tarragon leaves.
Put the Parmesan, lemon zest and tarragon leaves in a bowl. Add half the breadcrumbs with a good pinch of salt and pepper. Stir to mix. Crack the egg into a separate plate and whisk with a fork to break it up. Line a large baking tray with baking paper.
Press the whiting fillets into the egg, then the breadcrumbs. Turn them over a few times to coat evenly in the crumbs. Lay them on a baking tray. If there are any breadcrumbs left over, spoon them over the top of the fish.
Take the courgette tin out of the oven and add the cherry tomatoes. Put the courgette tin on the middle shelf of the oven. Put the fish on the top shelf. Bake for another 15 mins. The courgettes should be browned and the fish golden and flaking when you press it with a fork. Serve the fish with the roast veg and wedges of lemon for squeezing.