Heat oil in a large saucepan on a medium setting. Once the oil is hot, add onion, pepper flakes and a pinch of salt. Cook until onions become translucent, about 2 minutes.
Add sausage, breaking it apart with the back of a spoon, and cook for about 4 minutes, or until it is cooked through. Add garlic near the end of cook time to prevent burning.
Break lasagna sheets into halves and arrange atop meat. Add 3 cups of water and jar of pasta sauce. Cover pan and bring to a simmer. Stirring occasionally, simmer for 15 minutes over medium-low heat until pasta is al dente.
Remove mixture from heat and stir in Parmesan to incorporate. Season with salt and pepper to taste. Top with spoonfuls of ricotta cheese and cover. Allow dish to stand for 5 minutes.