Place the Brussels sprouts on a rimmed baking sheet, drizzle 1 tablespoon of the olive oil and the sambel olek over them, and toss to coat well. Season with salt and pepper and place into the oven. Roast for about 20 minutes until browned in spots and tender.
Meanwhile, season the steak generously with salt and pepper. Heat a large heavy skillet, such as cast iron over medium-high heat. Add the remaining tablespoon olive oil, and sear the steak for 3 to 4 minutes on each side for medium rare, which should have an internal temperature of 130°F. Remove the steaks to a cutting board and let them rest for 5 minutes before serving.
While the meat is resting, in a small bowl combine the mayonnaise, lemon juice, and parsley. Season with salt and pepper and stir well.
Serve the filets with the Brussels sprouts, and a dollop of the lemon mayo on the side.
Notes
A practical tip: If you don’t have a cutting board with a moat, think about buying one, especially if you cook meat often. The moat will catch those juices that a) you want to keep, and b) might run all over the counter and onto the floor, which is gross.