Preheat the oven to 350 degrees F (175 degrees C). Butter an 11x7-inch oven-proof casserole dish.
Place cooked, drained cauliflower florets into the prepared casserole dish and season with salt and pepper.
Melt butter in a small skillet over medium heat. Add garlic and cook and stir until fragrant, 1 to 2 minutes. Cut cheese into 1/2-inch cubes and add to skillet. Gently move cheese around the skillet until it starts to melt, 2 to 3 minutes. Add half-and-half and whisk until well blended, 1 to 2 minutes.
Stir in Parmesan cheese and remove from heat. Pour cheese mixture over cauliflower florets. Top with French fried onions, almonds, and crumbled bacon.
Bake in the pre-heated oven until bubbly, about 20 minutes.