Heat oil in a medium saucepan over a medium heat. Add onion and bacon and cook for 8 minutes or until onion is soft. Transfer to a bowl

To make the sauce, melt butter in saucepan over medium heat. Add flour and stir until well combined. Cook for 2 minutes. Reduce heat and milk slowly in batches, stirring constantly until well combined

When combined, increase the heat to medium and add mustard, and cheeses. Stir constantly until thick and mixture comes to the boil. Reduce heat to low and simmer for 4 minutes

Preheat oven to 180°C

Meanwhile, cook pasta in a large saucepan of salted water until just tender as per packet instructions. Drain and return to saucepan

Add bacon and onion mixture into the sauce along with the pasta and parsley. Mix to combine. Add 3/4 of the avocado and gently stir through pasta mixture

Transfer prepared pasta mix to a 10-cup capacity baking dish. Sprinkle remaining tasty cheese and parmesan over pasta. Bake for 25 minutes or until cheese topping is golden. Serve sprinkled with remaining avocado and green salad on the side