Spray a large frying pan with low-calorie cooking spray and set on a medium heat. Add the leek, pepper and garlic and fry for 5 minutes until just softening.
Add the asparagus, sugar snap peas, green beans and peas. Fry for a further 5 minutes.
Add the chopped tomatoes, tomato purée, balsamic vinegar, Henderson's relish and mixed herbs. Season to taste with salt and pepper, lower the heat and simmer for 10 minutes.
Preheat the oven to 190°C.
In a mixing bowl, combine the yoghurt and eggs. Season with salt and pepper.
Add half of the vegetable mixture to the bottom of the dish. Add 3 lasagne sheets and then half the yoghurt mixture. Repeat with the rest of the vegetables, lasagne sheets and yoghurt mixture. Sprinkle over the Cheddar cheese.
Pop into the oven for 30 minutes until the top is golden and bubbling. Serve!