If you search "dukan" in the minimins search engine I'm sure you will find ideas. I'm not familiar with that diet or I'd give you some of my own! Good luck!
There is a recipe section at the top of the Dukan Diet board - browsing there should give you some new ideas.
Do you eat lunch at home or at work?
If you need a packed lunch Dukan muffins are good. Or a slice of Dukan meatloaf. Stir dry-fried prawns are nice just add chopped garlic ginger spring onions and fresh coriander - good hot or cold.