In a large bowl or measuring cup, mix together the peanut butter, soy sauce, sriracha, coconut milk, and lime.
Once mixed thoroughly, set aside half as a dipping sauce. In the other half, mix in garlic, lemongrass, and green onion.
Cut up your flank steak and marinate it with the second half of the peanut sauce. Let it marinate in the fridge for at least 30 minutes.
Heat your oven up to 425F
In a large sheet pan, coat your vegetables and peanuts in some olive oil, salt, and garlic powder.
Spread it out evenly on a sheet pan.Once your beef is done marinating (this could also be done the night before), place it in a single layer on a rack on top of a sheet pan to catch the drippings.