Cook meat with onion. (Add oil as needed if meat is very lean.)
Add tomatoes, tomato paste and seasonings.
Cover and cook over low-medium heat for about 20 mintues, stirring occasionally, until liquid is reduced.
In separate medium saucepan, melt butter.
Whisk in flour, salt, and pepper.
Add milk, gradually
Bring to a boil, stirring constantly. Reduce heat and cook 1 minute.
Remove from heat and stir in half of shredded cheese. Set aside
Pour half meat mixture in greased 9 x 13 casserole dish.
Cover with half of lasagna noodles, then with remaining meat sauce. Top with remaining noodles. Pour white sauce over noodles, covering completely. Sprinkle with remaining cheese. Cover with foil.
Bake at 400°F for 40 minutes, or until noodles are done.