Heat olive oil in your Dutch oven.
Add ground beef and cook until brown.
Break meat into small pieces while cooking.
This takes about 8 minutes on medium heat.
Drain excess fat if needed.
Toss in diced onion and minced garlic.
Cook until onion turns soft and translucent.
This adds amazing flavor to your lasagna.
Stir frequently to prevent burning.
Pour marinara sauce into the Dutch oven.
Add Italian seasoning, salt, and pepper here.
Let it simmer for 5 minutes gently.
The sauce should smell absolutely wonderful now.
Mix ricotta, half the mozzarella, and Parmesan together.
Add the beaten egg to this mixture.
Stir in chopped spinach until well combined.
This creates your creamy cheese layer.
Spread some sauce on the Dutch oven bottom.
Break lasagna noodles to fit your pot.
Add a layer of noodles over sauce.
Spread cheese mixture over the noodles evenly.
Repeat layers until ingredients are used up.
Top with remaining mozzarella cheese generously.
Cover Dutch oven with its heavy lid.
Bake at 375°F for 45 minutes total.
Let it rest 10 minutes before serving.