Preheat your oven to 190°C (375°F). Line a baking tray with parchment paper. Peel and cube the sweet potato into roughly 3cm (1¼ inch) chunks. Place in a medium saucepan, cover with cold water, and bring to a boil.
Boil the sweet potato for 15–18 minutes until completely tender. Drain well and return to the pan. Add the butter and warm water or broth and mash until completely smooth — no lumps. A smooth mash is gentler on an inflamed stomach. Season with a pinch of black pepper. Cover and keep warm.
Place the cod fillets on the lined baking tray. Drizzle with olive oil and rub gently over the surface. Sprinkle dried thyme, parsley, and a pinch of black pepper over each fillet. Bake for 13–15 minutes until the fish flakes easily with a fork and is opaque all the way through.
While the cod bakes, slice the zucchini into rounds about 5mm (¼ inch) thick. Steam over boiling water for 5–6 minutes until tender but still holding their shape. Transfer to a bowl, drizzle with olive oil, and scatter fresh parsley over the top.
Spoon the sweet potato mash onto each plate. Place the baked cod fillet alongside and arrange the steamed zucchini rounds next to it. Finish with a light drizzle of olive oil over everything. Serve immediately.