For making meat sauce. Heat olive oil in a pan, add onions, garlic and green chillies. Saute this for a minute. Now add in carrots and bell peppers and stir fry for 2 to 3 minutes. Now add in tomato paste and cook that for 4 to 5 minutes till the flavours deepens. Now add in chicken along with oregano, basil, red chilli flakes, salt and sugar. Now add in marinara sauce and mix well. Cover and cook for 8 to 10 minutes. Add in chopped parsley and mix well.
Heat butter and olive oil in a pan, add flour and use a whisk to mix the flour into the butter. Cook the flour in the butter for 3 to 4minutes till raw smell leaves. now take the sauce pan from the heat, whisk in cold milk slowly so there is no lumps and keep cooking and mixing till it thickens. Now add in salt, white pepper powder, ground nutmeg and mix well. This is your bechamel sauce.
Preheat oven to 220 degree C ( 428 degree F).
Take a baking dish, spread meat sauce in the bottom. Place 3 lasagna sheets, spread meat sauce, Spoon some of the white sauce, sprinkle with mozzarella cheese, now place lasagna sheets on top and repeat this two more times. The top layer should be lasagna sheets with white sauce and mozzarella cheese. Cover the baking dish with a layer of parchment paper, followed with aluminium foil and cook for 40 mins in a 220 degree C ( 428 degree F) preheated oven. In the last 5 minutes of baking, remove the foil from the top, set the oven top broil mode and broil for 3 to 5 minutes.
Remove the baking dish from oven. Allow it to rest on the counter for at least 30 minutes. Now slice and serve the lasagna.