Heat the olive oil in a large skillet or Dutch oven over medium-high heat. Add the diced onion and sauté until translucent, about 5-7 minutes.
Add the minced garlic and cook for another 1-2 minutes.
Add the ground beef and Italian sausage, breaking it up with a spoon. Cook until browned, about 7-10 minutes. Drain any excess fat.
Stir in the crushed tomatoes, tomato sauce, tomato paste, Italian seasoning, and oregano. Simmer for about 20-30 minutes, allowing the flavors to meld.
Add salt and pepper to taste.
Optionally, add chopped fresh basil just before assembling the lasagna.