Heat olive oil in a large skillet over medium heat. Add onions and garlic, sauté until translucent, about 3-4 minutes.
Add ground beef to the skillet, cooking until browned and cooked through. Drain excess fat.
Stir in cinnamon, oregano, and nutmeg, cooking for another minute until fragrant.
In a separate saucepan, melt butter over medium heat. Whisk in flour and cook for 2 minutes to form a roux.
Slowly whisk in milk, continuing to stir until the sauce thickens, about 5-7 minutes. Remove from heat.
Layer the bottom of a baking dish with a thin layer of béchamel sauce, then noodles, ground beef mixture, spinach, feta, and mozzarella. Repeat layers, finishing with béchamel and mozzarella on top.
Cover with foil and bake for 30 minutes. Remove foil and bake an additional 15 minutes until golden and bubbly.
Let rest for 10 minutes before slicing and serving.
Notes
This Greek Comfort Lasagna can be made ahead and reheated. Leftovers taste great the next day!