Preheat oven to 375 °F (191 °C). Bring a large pot of water to a boil.
In a 9x5" loaf pan, lay bacon into the bottom of the pan with the sides hanging off the edges on either side. You will have to overlap some of the bacon pieces on top of each other and it's totally okay!
If your bacon keeps slipping, use clips to secure them to the side of the pan.
Add the lasagna noodles to the boiling water and cook until just tender/al dente. They will finish cooking in the oven. Put them directly into a ice water bath when done so the cooking process will stop and they will be cool enough for you to handle with your hands.
While the noodles are cooking, brown ground beef and onions together in a skillet then pour the marinara sauce into the skillet. Season with salt and pepper. Remove from heat and set aside.
Pat dry 1 lasagna noodle then place into the bottom of the loaf pan. Add a bit of the ricotta cheese in a thin, even layer, then add some of the ground beef mixture. Sprinkle a bit of the mozzarella cheese on top then repeat with the next layer.
Repeat until you have filled the loaf pan all the way to the top. Then, take the overhanging edges of your bacon and lay them on top of the lasagna, overlapping is okay.
Bake lasagna for 30-35 minutes or the bacon is crisp and cooked through.
Remove from oven and let sit for 20 minutes before removing and slicing to serve.