Preheat oven to 170c / 150c fan-forced. Heat oil in a frying pan and cook onions and bacon for 3-4 minutes until softened and bacon is slightly crispy.
Add mixed vegetables and cook for 2 minutes, stirring to thaw.
Remove mixture to a bowl. Mix remaining ingredients in a large bowl and mix in bacon and vegetable mixture.
Season with pepper and spoon into a greased and lined 28c, x 18cm brownie / slice pan.