Preheat the oven to 425 degrees F (218 degrees C).
Add 2 teaspoons of kosher salt to a large pot of water. Bring water to a boil, then add the Brussel Sprouts. Boil for 10 minutes, until bright green and tender. Drain the sprouts and lay them on a clean kitchen towel, patting them dry as much as possible.
While the sprouts are boiling, mix together the parmesan, garlic powder, smoked paprika, and cayenne pepper - set aside.
In a large bowl, toss the sprouts with a generous drizzle of olive oil (around 2 Tablespoons) until well covered in the oil.
Arrange the sprouts in a single layer on a baking sheet lined with parchment paper. Don't crowd the sprouts, making sure they're in a single layer not overlapping each other.
Using the bottom of a small glass press down on the sprouts to smash them flat. Sprinkle with a few pinches of kosher salt.
Put the sprouts in the oven and roast for 10 minutes. Flip them over carefully, then cover each one with your cheese mixture. Roast for another 5-7 minutes until the cheese is sizzling and crispy.