Preheat the oven to 180 degrees Celsius (356 degrees Fahrenheit).
In a large non-stick frying pan, add the olive oil and the yellow onions. Cook for about 5 minutes until the onion becomes translucent.
Add the beans, cajun seasoning, salt and tomato puree and mix well. Add a bit of water (about 1/2 - 1 cup), simmer for about 5 minutes then turn off the heat.
To a large baking tray add the corn chips, top with the bean mix and sprinkle on the grated cheese. Bake the nachos in the oven for about 10 minutes until the cheese has melted.