Preheat your oven to 400F and move the rack to the top third of the oven.
In a large, oven-safe skillet (use a skillet no smaller than 12"), add the sausage meat and onion and cook over medium-high until browned (about 10 minutes), breaking it up as you go along.
Stir in the garlic and cook for 30 seconds.
Add in the marinara sauce, broth, and oregano, and give it a good stir, then add in the lasagna noodles.
Once it starts to bubble again, reduce the heat so it's simmering fairly rapidly but not boiling like crazy. Let it cook until the noodles are bendy but not fully cooked (al dente) and the liquid has reduced considerably (it should look more like pasta sauce than soup). This should take about 15-20 minutes depending on how hot you're cooking it. Stir it every few minutes to ensure nothing is sticking to the bottom of the pan and that the noodles all get a chance to be submerged in the sauce as it tends to cook down fairly quickly. Adjust heat as needed to maintain a simmer. Important: don't rush through this step or the noodles won't end up fully cooked by the end.
Remove from the heat. Dollop on the ricotta (I just use a spoon), and then sprinkle the parmesan and mozzarella evenly over top. Bake, uncovered, for 10 minutes, and then broil for a few minutes to brown the cheese (watch it carefully).
Let it sit for 5 minutes, and then serve. Season with extra salt & pepper if needed. Fresh basil and/or parsley are delicious on top but totally optional!