Preheat the oven to 400°F.
Rub 1 tablespoon of the oil into the sweet potatoes and season with salt and black pepper, then place them on a baking pan and roast for about 40 minutes to 1 hour, depending on their size, until cooked all the way through. Let cool while you make the fishcakes.
Place the salmon fillets in a wide, shallow pan with the dill and peppercorns, and barely cover with water. Gently poach, uncovered, for 8 to 10 minutes until just cooked through. Lift the salmon from the poaching liquid and flake into a large bowl.
Halve the sweet potatoes, scoop out the flesh, and add to the fish along with the cilantro and lemon juice. Season well with salt and black pepper and mix together thoroughly. If you have the time, cover and chill the mixture in the fridge for 30 minutes to make the cakes easier to form. Shape the mixture into palm-sized cakes.
Put the flour, eggs, and matzo meal in 3 separate shallow bowls. Season the flour with salt and black pepper, then coat the cakes in the seasoned flour, dip into the beaten egg, and then roll in the matzo meal. Repeat the egg and matzo meal coating for a second time if you want an extra-crispy fishcake.
Place the fishcakes on a tray lined with nonstick parchment paper or foil and refrigerate until you are ready to fry.
Mix the ingredients for the lime za’atar yogurt together in a bowl, then cover and refrigerate until you are ready to serve.
Heat the remaining 2 tablespoons of oil in a wide skillet and fry the fishcakes, in batches, over medium heat for around 3 minutes on each side until they are nicely golden.
Serve with a generous spoonful of the yogurt on the side and a crisp salad.
Tip: If you can’t find matzo meal, you can substitute any other bread crumbs
of your choice; panko would be my next favorite.