Preheat oven to 350°. In a large pot of salted boiling water, blanch cauliflower, 3 minutes. Drain well.
In a large skillet, melt butter. Add garlic and cook until fragrant, 1 minute, then add flour and stir until golden.
Whisk in milk and bring to simmer.
Remove from heat and whisk in cream cheese. Once melted, stir in 1 cup cheddar cheese until melted. Add salt and pepper to taste.
Add drained cauliflower to cheese mixture and stir.
Add in all but 1 tablespoon each cooked bacon and green onions until combined.
Add to a buttered 9x13 baking dish then top with remaining cheddar, bacon, and green onions.
Bake 30 minutes or until cauliflower is tender and cheese is melted.