Preheat the oven to 180°C and line a 20cm x 9cm loaf tin with parchment.
Sift the flour, bicarbonate of soda, baking powder, and cinnamon together.
Beat the oil and sugar in a mixer, then add egg yolks one by one.
Fold in the grated beetroot, lemon juice, sultanas, and mixed seeds.
Mix the flour blend into the egg mixture on a slow setting.
Beat egg whites until stiff and gently fold into the batter with a metal spoon.
Bake for 50-55 minutes, covering with foil after 30 minutes.
Cool the cake in the tin for 20 minutes before transferring to a wire rack.
Mix icing sugar with lemon juice to a drizzling consistency.
Drizzle icing over the cake and scatter with poppy seeds.