Preheat the oven to 200°C (400°F) with a rack in the centre.
Put the potatoes in a pot of cold salted water, bring to a boil over high heat and simmer over medium heat until tender when pierced, about 15 minutes. Drain.
In a 23 x 33 cm (9 x 13 inch) baking dish, toss the cherry tomatoes, olives, capers, sliced red onion and garlic with the oil and oregano.
Roast the tomato mixture for 10 minutes until the tomatoes start to burst.
Pat the cod dry, season with salt and pepper, and nestle the fillets into the tomatoes. Drizzle with the lemon juice and spoon a little of the juices over the fish.
Bake for 10 to 12 minutes, until the cod is opaque and flakes easily with a fork, 63°C (145°F) in the thickest part.
Scatter with parsley and serve with the potatoes, spooning the tomato and olive sauce over everything.
Made it? Rate it
Your rating helps other lifters pick their next meal.
Tips
Haddock, pollock or tilapia work the same way.
Swaps
Low-FODMAP: leave out the onion and garlic and use garlic-infused oil.