Chop the onion finely - I use my Pampered Chef chopper
Put the onion and meat in a frying pan. Brown the meat, seasoning it with Italian seasoning, garlic, salt and pepper. I just sprinkle everything until it smells "Italian."
Drain off any fat.
Drain most of the juice from the diced tomatoes and add the two cans to the browned meat.
Let simmer for about 8-10 minutes, stirring often.
Add jar of spaghetti sauce and let simmer for 20-30 minutes on low, stirring occasionally. You want the meat, tomatoes and sauce to get a lot of flavor and the simmering does this. You can't really simmer too long. Just let it simmer while you do the next steps.
While the sauce is simmering, go ahead and chop all your spinach finely with a chopper.
Boil your noodles in a large pot (so you can use it to mix all the ingredients.)
Once your noodles are cooked, drain the water.
Add 1 bag of cheese to the pot of hot noodles and stir so the cheese starts to melt.
Stir in the spinach.
Stir in the meat sauce.
Pour everything into your pans - this usually makes an 11x17 and an 8x8 pan of pasta for me.
Sprinkle the tops of both pans with the other half bag of cheese.
Bake for 30 minutes at 375 so everything can bake together and the cheese will melt on the top.