Preheat the oven to 400 degrees F (200 degrees C). Line a baking sheet with parchment paper.
Trim off the bottom of the cauliflower stem to create a flat surface. Place cauliflower head onto a cutting board with the stem side facing down; cut the cauliflower vertically into 1 to 1 1/2-inch thick slices. Remove any tough stem pieces. Cut the slices into smaller pieces, about the size of florets. Place on the baking sheet and drizzle with olive oil.
Roast in the oven for 10 minutes; flip pieces over and roast for 10 minutes more.
Meanwhile, cut butter into 4 pieces. Melt in a small saucepan over medium heat, stirring constantly until butter begins to brown, 4 to 5 minutes. Butter will foam up, then subside. The butter should have a nutty aroma. Stir in garlic and continue stirring for 15 to 20 seconds. Add in capers and lemon pepper. Remove from heat.
Spoon brown butter over the roasted cauliflower and serve.