Drizzle the cauliflower and red onion generously with olive oil, and season with salt and pepper.
Roast the vegetables in the preheated oven for 15 minutes.
Cook the bacon lightly in a pan until golden, remove from heat, let cool, and chop into smaller pieces.
Add the grated Dill Havarti Cheese over the cauliflower and onions after their initial 15-minute roast, then return to the oven for about 10 minutes until the cheese melts.
Top with the chopped bacon and roast for another 5 minutes.