In a medium skillet, cook the bacon over medium-high heat until crisp. Transfer the bacon to a paper towel-lined plate to cool & set aside. Reserve 1/4 cup of bacon grease.
Preheat oven to 425 F. Line a baking sheet with parchment paper. Set aside.
In a large bowl, combine the cauliflower, bacon grease, garlic powder & black pepper. Toss to combine.
Spread cauliflower on the prepared baking sheet, then bake for 18-22 minutes, flipping once halfway through. The cauliflower should be tender & golden brown when ready.
Sprinkle the cheddar cheese on top of the cauliflower & bake an additional 2-3 minutes to melt the cheese.
Remove from oven & top the cauliflower with the crumbled bacon & green onions. Drizzle with ranch dressing. Serve immediately.