In a large nonstick pan (10–12 inches), heat oil over medium heat. Once shimmering, add in onion. Sauté until onion is translucent, about 3–4 minutes.
Turn heat to high and add sausage and salt/pepper to taste. (I add 1/2 teaspoon salt and 1/4 teaspoon pepper.) Cook, breaking/crumbling it up as you cook with a wooden spoon until sausage is browned and cooked through. If there is a lot of grease, drain it off or dab the meat with a paper towel. Add garlic, stir, and cook for 30 seconds.
Add undrained diced tomatoes and marinara. Bring the mixture to a rapid simmer, then reduce heat to medium. Let simmer about 5 minutes, stirring occasionally, while preparing the cheese filling. Taste and season if needed (more salt/pepper). Transfer all but 1 cup (135g) meat sauce to a separate bowl.
In a separate bowl, whisk the eggs with a fork. Stir in ricotta, basil, Italian seasoning, 1/2 cup (50g) mozzarella cheese, and 1/4 cup (15g) Parmesan cheese. Stir to combine and season to taste with salt and pepper. (I add 1/4 teaspoon pepper and 1/8 teaspoon salt.)
Spread 1 cup (220g) of the cheese mixture over the meat sauce in the pan. And 1 and 1/2 cup (395g) of the meat sauce on top. Place 3–4 of the uncooked lasagna noodles on top of the meat sauce. Break up the pasta as needed and make sure it is in an even layer (don’t overlap—pasta won’t get tender). Pour 2 tablespoons of hot water evenly over the pasta.
Add the rest of the cheese mixture on top. Add 1-3/4 cup (455g) of the meat sauce in an even layer on top of the cheese. Add remaining 3–4 uncooked pasta noodles (breaking to fit the pan) on top of the meat sauce. Pour the remaining 2 tablespoons of very hot water evenly over the pasta. Add the last of the meat sauce (about 1-3/4 cups; 370g) on top.
Bring to a boil. Reduce heat to medium low (it should be a gentle simmer at the edges) and cover pan with lid (or foil in a pinch). Simmer, covered, 20–25 minutes (see note 2). Remove from heat and let stand, still covered, for 10 minutes (this is when the pasta finishes cooking). Remove lid and sprinkle with remaining 1/2 cup (50g) mozzarella cheese and remaining 2 tablespoons Parmesan cheese. Cover and let stand 2 minutes or until melted. Cut into slices (it’s a little messy!), serve, and enjoy!
Notes
Note 1:No-cook/boil lasagna: In order for the pasta to cook through in time, you'll need to use the right kind of pasta. The package will call out either “oven ready” or “no boil/cooking required.”Note 2: For simmering, there should be a gentle bubble along the edges of the pot. If there is no movement, the lasagna won't cook through (temperature is too low) and too much movement (heat too high) the dish will dry out. Avoid checking pasta too often; this lets out the steam.Storage: Let the dish cool completely before covering with plastic wrap or foil. Store in the fridge for up to 4 days. You can freeze it in a container or wrapped in foil for up to 3 months.