Preheat oven to 375°F (190°C) and lightly grease a baking dish.Heat olive oil in a skillet and cook diced onion until soft.Add minced garlic and cook for 30 seconds.Add ground beef and cook until browned, breaking it apart while cooking.Stir in taco seasoning, salt, pepper, tomato sauce, and diced tomatoes.Add softened cream cheese and mix until melted and creamy.Transfer the beef mixture to a baking dish and spread evenly.Sprinkle half the shredded cheese over the mixture.Add the remaining cheese on top to form a cheesy layer.Bake for 15–20 minutes until the cheese melts and becomes bubbly.Remove from the oven, cool slightly, then slice and serve.