Slice the tofu into thin strips and sauté in olive oil until browned.
In a separate pan, heat olive oil and stir-fry onions, carrots and turnips until soft. Add tofu and leeks and season with salt and pepper to taste. Chill the mixture in the refrigerator for a few minutes.
Add Boursin into the mixture and divide resulting mixture equally into each spring roll sheet and wrap them. Deep fry for 3-4 minutes on medium heat.
Drain the rolls on clean paper towels. Cut each roll into two pieces and serve.