Preheat oven to 400°; remove baguette from bag + bake 7-10 min til warm; slice in half lengthwise

Meanwhile, heat 1 tbsp oil in skillet over med-high; pat steak dry, season with salt/pep + sear 4-5 min per side for med-rare; rest 5 min then thinly slice

Heat 1 tbsp oil in skillet over medium; thinly slice onion + sauté 8-10 min until browned; season with salt + add 2 tbsp water; cover + cook 3-5 min until softened

Spread bottom slice of baguette with ¼ cup sauce then top with steak + onions; close the sandwich + cut in half; divide to plates—nice job, chef!