In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes.
Stir in the minced garlic and cook for an additional 1 minute until fragrant.
Add the ground beef or lamb to the skillet, breaking it up with a spoon. Cook until browned, about 5-7 minutes. Drain excess fat if necessary.
Stir in the diced tomatoes, tomato paste, oregano, basil, cinnamon, red pepper flakes (if using), salt, and pepper. Bring the mixture to a simmer.
Reduce the heat to low and let the sauce simmer for 20-25 minutes, stirring occasionally. Adjust seasoning to taste.
Serve the meat sauce over cooked pasta or rice and garnish with fresh parsley.