Cooking flaky white fish in a bag of foil or parchment paper serves 3 purposes, both locking in and forcing the ingredients to mingle, gently steaming the fish and also cutting down washing up to a minimum. Make sure to scoop up the juices that will have collected at the bottom, as the pesto will have had time to release all its rich, complex flavours.
Heat and oven to 180C fan / 190C non fan.
Tear off a piece of foil large enough to wrap the fish and with enough space for allow the air steam to expand, and then do the same with parchment paper, but slightly smaller. Lay the foil on a baking sheet or roasting tray, then place the parchment paper down, keeping it to one side of the foil, with the aim of eventually folding the foil over.
Pour the olive oil onto the base, then place the thyme on the bottom and lay the fish on top. Next scatter the chickpeas and cherry tomatoes over the top and season well with salt and pepper. Now place blobs of the pesto all around and on top of everything. Fold the foil over to form an envelope and crimp the edges together using small folds along the edge, so that no steam will escape.
Place in the oven and bake for 15 minutes. Remove from the oven and carefully prize the foil open, taking care as steam will escape when you open it. The fish should have turned white and feel firm to the touch. If you’re unsure, carefully cut open the middle of one piece to check if the fish is cooked all the way through. Divide the cod and other ingredients between bowls and spoon over plenty of the juice that will have collected.