Brush the bread with oil and crisp in a toaster or in an oven at gas 6, 200ºC, fan 180ºC, for a few minutes. Season with salt and pepper.
Put the beetroot in a bowl with the crème fraîche, dill and half the spring onions. Season and gently fold together. Divide the mixture between the toasts, then top with the flaked smoked mackerel. Sprinkle over the remaining spring onion and extra dill and serve.