1. Preheat your oven to 200°C/Fan 180°C/Gas 6. Scrub the sweet potatoes and chop them into 1-2cm-thick chunks (no need to peel unless you want to). Tumble into a large roasting tin (see our tip, below, about what size tin you need). Trim the carrots and cut them lengthways into halves or quarters depending on thickness. Add to the tin. Cut the stalk off the broccoli and chop it into finger-sized lengths. Cut the broccoli head into large florets and add all the broccoli pieces to the tin. Pour over 2 tbsp oil and season with a generous pinch of salt and pepper. Toss to coat. Pop the un-peeled garlic cloves on top. Slide the veg into the oven for 25 mins.
2. While the veg roast, peel and thinly slice the red onion and place it in a small bowl. Grate in the zest from the lemon and squeeze in the juice from half. Add a pinch of salt and use your hands to scrunch the onion for 1-2 mins. Set aside to lightly pickle.
3. Peel and finely grate the ginger into a large dish or bowl. Squeeze in the juice from the remaining lemon half. Add the brown rice miso and the tamari with 1 tbsp oil and mix well. Set to one side.
4. When the veg have roasted for 25 mins, remove the tin from the oven and lift out the roast garlic cloves. Slide the tray back into the oven for another 10 mins.
5. Let the garlic cool for a couple of mins then squeeze the roasted flesh from the papery skins into the dish with the miso mixture. Use a fork to mash it all together. Lay the cod fillets in the dish and turn them over a few times to coat them in the miso marinade.
6. Remove the tin from the oven. Make 4 spaces for the cod to by pushing the veg to the sides. Pop the cod fillets in the spaces. Drizzle the remaining miso marinade over the veg.
7. Slide the tin back into the oven for 10-15 mins till the fish is cooked. Check by lightly pressing the fillets with the back of a fork. They should be opaque and flake easily. The veg should be roasted and tender, the broccoli florets lightly browned and crisped. Cook for a little longer if you need to.
8. While the tin roast cooks, finely chop the coriander stalks and add to the bowl with the quick-pickled red onion.
9. When the fish and veg are ready, divide them between 4 warm plates. Top with the pickled red onion and the coriander leaves to garnish.
If your roasting tin looks a little overcrowded, with the veg are piled up on top of each other, you can spread them between 2 tins or baking trays. Keeping a little space in the tin, with everything in 1 layer helps the ingredients cook evenly, and also helps the veg to crisp up. The tray on the lower shelf in the oven may need a little longer to cook, so swap them over halfway through cooking.