Preheat the oven to 375°F (190°C).
Heat olive oil in a large skillet over medium heat.
Add diced onion and cook for 3-4 minutes until translucent.
Add minced garlic and cook for 1 minute until fragrant.
Add ground beef to the skillet and cook until browned, breaking it apart with a spatula, about 6-8 minutes.
Drain excess fat from the skillet.
Add diced green bell pepper, chopped cauliflower, and sliced mushrooms to the skillet. Cook for 5-7 minutes until vegetables are tender.
Stir in dried oregano, dried basil, salt, and black pepper. Mix well.
Remove skillet from heat and stir in sour cream and heavy cream until fully combined.
Transfer the mixture to a 9×9 inch casserole dish and spread evenly.
Sprinkle shredded cheddar cheese evenly over the top.
Bake in the preheated oven for 20 minutes or until the cheese is melted and bubbly.
Remove from oven and let cool for 5 minutes before serving.