Preheat oven to 375°F (190°C).
Steam or boil cauliflower florets until tender, about 5-7 minutes; drain well.
Blend cauliflower with heavy cream, cream cheese, salt, and pepper until smooth and creamy.
Heat olive oil in a skillet over medium heat, then sauté garlic until fragrant.
Add shrimp to the skillet and cook until pink and opaque, about 3-4 minutes, seasoning with Cajun seasoning, salt, and pepper.
Grease a 9x13-inch baking dish; spread the cauliflower mixture evenly, then layer the shrimp on top.
Sprinkle shredded cheddar cheese over the shrimp and bake for 20-25 minutes until cheese is melted and bubbly.
Remove from oven and garnish with green onions before serving.