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 softened.
Add minced garlic and cook for 1 minute until fragrant.
Add ground beef to the skillet and cook, breaking it apart with a spoon, until browned and cooked through, about 6-8 minutes.
Drain any excess fat from the skillet.
Add diced green bell pepper, diced zucchini, and chopped cauliflower to the skillet. Cook for 5-6 minutes until vegetables are tender.
Stir in dried Italian seasoning, salt, and black pepper.
Remove skillet from heat and stir in sour cream and heavy cream until well combined.
Transfer the mixture to a 9×9 inch casserole dish.
Sprinkle shredded cheddar cheese evenly over the top, then sprinkle shredded mozzarella cheese.
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.