Spray a large frying pan with low-calorie cooking spray and place over medium heat.Add the onion and garlic, frying until softened. Add a splash of water if they stick.
Stir in the yellow pepper, sliced carrots, mushrooms, and grated courgette. Cook for 5 minutes. Again add some water if needed.
Add the broad beans, red lentils, chopped tomatoes, tomato purée, oregano, basil, and vegetable stock. Mix well.Simmer for 20 minutes, stirring occasionally, until the lentils are soft and the mixture has thickened. Season to taste.
Preheat the oven to 180°C (fan 160°C) or Gas Mark 4.
Meanwhile in a bowl, whisk together fat-free yoghurt, beaten eggs, mustard powder, and some salt and pepper.
Spread a layer of the lentil mixture in a lasagna dish. Top with lasagna sheets. Repeat layers, finishing with a layer of lasagna sheets depending on the size of your dish. Pour over the yoghurt sauce, ensuring the top layer is fully covered.
Sprinkle grated cheddar over the top.
Bake for 30–35 minutes until golden and bubbling.
Let the lasagna rest for 5 minutes before serving. Enjoy with a crisp salad or steamed veggies.