Heat oil in a non-stick frying pan over medium heat. Cook schnitzel for 4 minutes on each side or until crisp, golden and cooked through. Drain on paper towel. Cool; slice thinly.
Combine wombok and vinegar in a small bowl; season.
Lay a sheet of baking paper on a chopping board; top with bread. Spread each slice with butter; turn so buttered-side faces down. Top 2 slices of bread each with 2 slices of cheese, half the schnitzel and half the wombok mixture. Top with remaining bread, buttered-side up.
Preheat a sandwich press; toast sandwiches in hot sandwich press for 5 minutes or until cheese melts and bread is golden and crisp. Serve toasties with avocado dip, if you like.