Preheat oven to 350 degrees Fahrenheit.
Heat oil in a skillet over medium-high heat.
Add ground beef and cook, using a wooden spoon to break up.
Once the ground beef has started to brown and is broken up into small pieces, add onion, garlic, and Italian seasoning to pan. Season to taste with salt and pepper. Cook until the meat is brown and onions are tender about 7 to 8 minutes.
Stir in marinara and simmer for 3 to 4 minutes.
Meanwhile, cook the spaghetti according to package instructions.
Drain and return to the hot pan. Toss with the ricotta cheese.
Place a spoon full of the meat sauce in the bottom of a 13 x 9” casserole dish. Top with half of the noodles, half of the sauce and half of the cheese. Repeat the layers, ending with the cheese.
Bake for 25 to 30 minutes, until warm and bubbly.