Preheat the oven to 190°C/275°F/gas mark 5. Grease a 900g (2lb) loaf tin and set aside. Fry the onion gently for 10-15 minutes until softened, stirring occasionally. Remove from heat and leave to cool.
Place the maize meal, rice flour, soya flour, baking powder, sugar and salt in a bowl and mix well. Stir in the cheese. In a small bowl, beat together the milk, eggs, and melted butter, then add to the flour mixture, stirring to mix well.
Reserve about 1 tablespoon of the cooked onions. Stir the remaining onions into the bread mixture. Transfer the mixture to the loaf tin and level the surface. Sprinkle the reserved onions over the top.
Bake for about 30 minutes, or until the loaf is risen and golden brown. Turn out and cool on a wire rack. Serve warm or cold in slices.