1. Heat the oil in a large saucepan and sauté the onion for 5 minutes or until softened.
2. Add the beef mince and cook for 5-8 minutes or until lightly browned (skip this step if you are making a vegan friendly option).
3. Add the tomatoes, beans, Vegemite, tomato paste, chilli flakes and water. Stir to combine and simmer gently for 20-30 minutes or until thickened.
4. Meanwhile, place avocado in a bowl and use a fork to mash until smooth. Add lemon juice, diced tomato, pepper and stir until combined. Set aside.
5. Preheat grill on medium.
6. Place Cornchips into an ovenproof dish. Top with chilli beef mince OR bean mix and sprinkle with cheese of choice.
7. Cook under grill for 4-5 minutes, or until cheese of choice is melted and golden brown.
8. Serve with avocado, your choice of sour cream and fresh coriander.