Heat butter in a pan, add flour and stir fry for a min. Add milk slowly and keep mixing till it thickens.
Add in salt, pepper and mix well.
Heat olive oil in a pan, add onions, garlic, carrots, tomatoes and saute for 2 mins.
Cover and cook till tomatoes are cooked.
Add chicken and other spices and mix well.
Add in ketchup and water and mix well. Cook till sauce thickens.
Take a baking dish, spread tomato sauce in the bottom. Place lasagna sheets. Top with white sauce. Top with more tomato sauce, then mozzarella cheese. repeat this two times.
The top layer should be white sauce. Top with cheese.
Cover with foil and cook for 40 mins in a 180 degree c oven.
Now remove the cover, place it in grill mode and cook for 5 mins till top is golden brown.