Preheat oven to 425 F. Option to line a baking sheet with parchment paper for easy clean up. Brush some of the oil onto your baking sheet or parchment paper.
Prep the cauliflower, by rinsing it, removing the outer leaves, and trimming the bottom of the stem (keep the core!). Slice cauliflower in half, then working from the center, slice 1" steaks--I'm usually able to get 3-4 steaks per head of cauliflower. The cauliflower will fall apart, you can save these florets for another recipe, or bake them on a second baking sheet (you'll need to double the oil and seasoning if you want to bake them all together).
Place the cauliflower steak in a single layer on your prepared baking sheet, be sure to leave a little space between each. Brush the tops with 1/2 the oil, and sprinkle with half the salt, pepper, garlic powder, and smoked paprika.
Bake in preheated oven for 15 minutes.
Remove from oven, flip each steak, and brush the second side with the remaining seasoning. Sprinkle with remaining salt, pepper, garlic powder, and smoked paprika. Return to the oven and continue to bake until the cauliflower has softened to your liking, should be between 12-15 minutes.
Option to make the aioli while the cauliflower is roasting, then drizzle it on top, or serve it as a side to dip. Enjoy!