In a large frying pan, heat 1 tbsp oil over a medium heat. Add the onion and cook for 5 minutes. Add the chicken and cook for a further 5 minutes. Stir through the peas, asparagus, beans, broccoli and baby corn, as well as half the cherry tomatoes. Remove from the heat and set aside.
Preheat the oven to 200ºC/fan 180ºC/gas mark 6. Add the remaining oil and the flour to a saucepan. Mix to form a paste then cook over a low heat for 1 minute, stirring, before gradually whisking in the milk. Stir continuously until thickened. Bring to the boil, then reduce to a simmer for 5 minutes. Stir in half the cheese, then remove from the heat and stir in the chopped parsley.
Add one-third of the chicken and vegetable mixture to an ovenproof dish. Place a layer of lasagne sheets over the top, then spread over a layer of the white cheese sauce. Repeat until you have used everything up, finishing with a layer of sauce. Scatter the remaining cheese over the top, followed by the remaining cherry tomato halves, cut-side up. Bake for 30 minutes until golden and bubbling.