Cook pasta according to package directions.

Preheat oven to 375F.

Heat the oil in a large non-stick frying pan over medium-high heat. Add onion and cook, stirring occasionally, for 5 minutes. Add ground meat and cook, stirring occasionally, for 10 minutes, or until the meat is cooked through (no longer pink). Add minced garlic, 3/4 tsp salt and 1/4 tsp pepper. Stir for 1 minute.

Add the tomato sauce to the meat on the frying pan and mix until combined. Add the cooked pasta to the meat with tomato sauce and mix until combined. Remove from heat.

In a mixing bowl, mix ricotta cheese, egg and 1/4 tsp salt.

Prepare a non-stick large baking pan (I use the glass Pyrex). Divide the pasta mixture into 2 parts. Put 1 part of the pasta mixture in the baking dish, and spread so it's an even layer. Spread the ricotta mixture on top of the pasta. Put the remaining pasta mixture on top of the ricotta layer. Sprinkle the top of the casserole with shredded cheese.

Put the assembled casserole in the oven and bake for 40 minutes.