Whisk together all of the Marinade ingredients in a spouted measuring cup. Pour all but 1/3 cup of the marinade into a large ziplock bag, set bag aside. Cover and reserve the remaining 1/3 cup marinade in the fridge.
Add the steak to the ziplock bag with the marinade and securely close it. Gently massage the steak through the bag to evenly coat it in the marinade. Then lay the bag flat on a large plate and put it in the fridge for the steak to marinate overnight (10-24 hours).
Remove the steak from the fridge roughly 15 minutes before you plan to grill (you just want to take the chill off the outside of the meat, but keep the center cold so that it develops a nice exterior crust and medium-rare interior). Pre-heat your grill to a medium-high temperature (450-500°).
Meanwhile, whisk together the reserved 1/3 cup marinade (stored separately from the steak) and 1 tablespoon olive oil in a large bowl. Add the shaved Brussels sprouts to the bowl and let them hang-out at room temperature until ready to finish.
Pull the steak from the ziplock bag (discard bag and residual marinade) and place it on the pre-heated grill. Close the lid and let the steak sear on one side for 4-5 minutes. Then flip the steak and let it sear on the opposite side for another 4-5 minutes (lid closed). When nicely browned on the outside and pink inside (medium-rare), pull the steak from the grill and let it rest at room temperature for 5-10 minutes.
As the steak is resting, heat the remaining 2 tablespoons olive oil over medium-high heat in an extra large skillet. Let the pan and oil get screaming hot (about 2 minutes) so that when you add the sliced asparagus pieces they immediately sear. Spread the asparagus pieces across the hot pan (work in batches if needed) and resist the urge to toss or flip them for at least 2 minutes. When lightly browned on one side, give them a quick toss and sear the other side (another 1-2 minutes). Remove the asparagus pieces from the pan while they are still pretty firm, bright green, and seared in spots. Immediately add them to the bowl with the Brussels sprout shavings and dressing. Toss to evenly distribute and coat in the dressing.
Lastly, add the 3/4 teaspoon kosher salt, 18 teaspoon fresh ground black pepper, and Manchego shavings to the asparagus and Brussels sprout salad and briefly toss. Divide among 4 plates or spread across a shallow serving bowl or platter. Cut the steak against the grain into thin slices and arrange them alongside or on top of the salad. Generously drizzle the prepared Dirty Chimichurri Sauce over the steak or serve on the side. Enjoy!
TIP A: If you have a food processor with a slicing blade, then you can shave 10 Brussels sprouts in about 15 seconds flat. If not, then a good knife works equally well or you can often find Brussels sprouts pre-shaved in your grocer's produce section (near the packaged lettuce). Another shortcut favorite of mine is to use Mann's® Power Blend which includes a mix of shaved Brussels sprouts, cabbage, kale, carrots, broccoli, and kohlrabi. If Brussels sprouts are not your thing, then a blend of hearty mixed greens is delicious too.