Preheat oven to 400°, mix halved brussels with 1 tbsp oil + season with salt/pep; place on a sheet pan on the top rack + roast 17-25 min til golden

Heat lightly oiled skillet over med-high; pat meat dry, season with salt/pep + sear 2-3 min undisturbed til browned; flip meat + sear 2-3 min more for medium-rare (for more well done, increase cook time 1-2 min per side)

Pour contents of mashed cauliflower into a microwavable-safe dish + cover with a damp paper towel; cook high 1-2 min until hot; stir + serve; divide to plates