In a bowl, add all the ingredients for the marinade and mix together thoroughly. Add the marinade to a larger food safe bowl or into a food safe bag. Take your tri-tip and score the fat cap in a cross hatch pattern about ⅛” apart. Add the tri-tip to the marinade and place in the fridge for at least 4 hours, but ideally 8 hours.
Preheat a medium heat fire (about 350F) for direct grilling. Bonus: use a Santa Maria style grill in order to raise and lower the grill grate to help maintain an even cooking temperature.
Pull your tri-tip out of the fridge to come to room temperature for about 20 minutes. Pull the steak out of the bag and discard the excess marinade. Add the steak to the grill with the fat cap side down. Render the fat cap for about 7-8 minutes before flipping over. Cook the tri-tip for about 25-30 minutes flipping every 7-8 minutes until it reaches 130F for medium-rare. When you are about 7-8 minutes before being done, add your green onions to the grill to char for about 3-4 minutes per side. Once the steak and green onions are done, pull it off and let it cook for at least 10 minutes.
As the steak rests, mix together all the ingredients for the Peanut Butter Sauce. Add water as needed for your desired consistency. I added about 2.5 tbsp of water for my sauce.
Once the steak is done resting, slice the tri-tip against the grain. Serve sliced with the charred scallions, limes and a drizzle of the Peanut Butter Sauce. Enjoy!