Heat the oven to 375 F. Heat the olive oil in a frying pan and add the leeks with a good pinch of salt. Cook for 8-10 minutes or until really soft.
Add the garlic to the leeks and cook for 2 minutes. Keep 4 tbsp of the ricotta aside then stir the rest into the leeks. Add the chicken. Mix everything well then add enough vegetable stock to make it a little saucy but not watery. Take off the heat.
Put a 1/4 of the sauce in the bottom of an oiled 8x8 baking dish.
Top with pesto, then 2 sheets of lasagna. Repeat 3 times, ending with lasagna.
Mix the rest of the ricotta with another splash of vegetable stock and any additional pesto and spread over the top layer.
Scatter over the parmesan and bake for 40-45 minutes until golden and bubbling.
The 40 minute baking time is dependent upon no-boil lasagna. If using traditional lasagna boiled beforehand, reduce the baking time to appx. 20 minutes.
You can also make this vegetarian! Just cut out the chicken and add extra veg: cooked kale, such as in the original recipe, would be best.