Preheat oven to 425°
Season the cauliflower steaks with 1.5 tbsp olive oil, salt, pepper, lemon zest, and dried oregano. Lay them on a parchment paper-lined baking sheet and roast for about 30 minutes flipping 1/2 way through with a spatula.
Meanwhile, on a medium skillet, add the remaining 1 tbsp olive oil. Add the garlic and saute for 30 seconds. Add in the mushrooms and cook for another 4-6 minutes until soft.
Add in the capers, white wine, lemon juice, and butter. Melt and cook for 2-3 minutes. Remove from heat.
To plate, add the cauliflower steaks then drizzle some of the lemon-caper sauce right on top. Garnish with parsley and serve.