Preheat your oven to 180°C/160°C fan/gas mark 4.
Heat some olive oil in a large pan over medium heat, then add the onions and garlic. Cook until the vegetables become soft.
Add the chopped chicken to the pan and cook, stirring occasionally, for 5-7 minutes or until browned all over.
Stir in the chopped tomatoes, oregano, basil, salt, and pepper. Add the tomato paste and mix everything together. Cook for 10-15 minutes or until the chicken is cooked through.
Meanwhile, make the béchamel sauce. Melt some butter in a saucepan over low heat, then add the flour. Stir continuously until the mixture becomes smooth. Gradually pour in the milk while stirring continuously until the sauce becomes thick and smooth. Season with salt and pepper.
Take a deep baking dish and spread half of the chicken mixture on the bottom. Cover the mixture with a layer of no-cook lasagne sheets, then pour a layer of béchamel sauce on top of the chicken.
Repeat with another layer of lasagne sheets and the remaining chicken mixture, then add one final layer of lasagne sheets and top with the remaining béchamel sauce.
Sprinkle some grated mozzarella cheese on top of the lasagne.
Bake for 20 minutes or until the cheese is melted and golden brown.
Let the lasagne cool for a few minutes before slicing and serving.