Blend one onion, bell pepper, garlic, and tomato paste.
Season the ground beef and in a hot skillet with oil, brown the meat.
Once browned, add the blended mix, and also add some bay leaves, a pinch of thyme, and oregano.
When it starts to boil, reduce to medium heat and cook for 15 minutes until the sauce thickens. Set aside.
Separately, make the bechamel sauce. Boil the milk with ½ cup of water (or chicken broth), the other onion, butter, salt, and pepper. When boiling, dissolve the wheat flour in a bit of cold milk or water and add to the mix, stirring continuously to prevent lumps. Keep stirring until it thickens.
To assemble the lasagna, in an ovenproof dish, spread a bit of the bolognese sauce at the base; place a layer of lasagna pasta, then more bolognese, some bechamel, and cheese slices. Add another pasta layer and repeat until you have three layers.
Finish with a lasagna pasta layer and cover generously with bechamel. Sprinkle parmesan on top and bake at 355°F (180°C) for 30 minutes.