Whisk together olive oil, soy sauce, Sriracha, mustard, ginger and garlic powder until well blended. Place Brussels sprouts in mixture and let sit for 3 to 6 minutes.
Preheat a large stovetop pan over medium high heat. Once heated, place Brussels sprouts and sauce in the pan, flat side down, pouring any sauce over sprouts. Cook for about 7 to 9 minutes or until bottoms are browned. Stir sprouts around, cooking for about 5 more minutes or until they are tender when poked with a fork.