Peel the sweet potatoes and cut into 2cm chunks. Put in a medium saucepan of cold salted water and bring to the boil. Reduce the heat to medium and cook for 12-14 mins until tender. Drain, then return to the pan and mash until smooth. Season with salt and pepper.
Step 2 — Prep ingredients
Meanwhile, lightly grease a 1L (4 cup) baking dish. Thinly slice the spring onions. Crush or finely chop the garlic. Cut the fish into 3cm chunks. Crumble 1 stock cube* into a heatproof jug, add the pepper and garlic seasoning and 180ml (¾ cup) boiling water and stir to dissolve.
Step 3 — Make sauce
Heat 1 tbs olive oil in a medium deep frypan over medium-high heat. Cook the spring onion and garlic, stirring, for 1-2 mins until softened. Add 1 tbs plain flour and cook, stirring, for 1-2 mins until golden. Gradually add the stock and 60ml (¼ cup) milk and cook, stirring constantly, for 3 mins or until starting to thicken.
Step 4 — Add peas and fish
Add the peas to the sauce, then bring to the boil and cook, stirring, for 2 mins or until the peas are tender and the sauce is thickened. Add the fish, then reduce the heat to medium and cook for 3 mins or until the fish is just cooked through. Remove the pan from the heat. Taste, then season with salt and pepper.
Step 5 — Grill pie and serve up
Meanwhile, preheat the grill to high. Transfer the fish mixture to the baking dish. Top with the sweet potato mash. Put the breadcrumbs and 1 tbs olive oil in a bowl and toss to combine. Scatter over the pie. Grill the pie for 4 mins or until the breadcrumbs are crisp and golden. Divide the fish pie among bowls and enjoy!
Step 6 — Make it yours
Like it herby? If you have some on hand in the crisper drawer or veggie garden, scatter over a handful of coriander or parsley leaves before serving.