Break the spaghetti noodles in half and place in the Instant Pot. Add the garlic, coconut oil, 1 teaspoon salt, and water. Cover and lock the lid into place.
Set the Instant Pot on "Pressure Cook High" for 4 minutes. Once it is finished cooking, turn the Instant Pot "Off", then press the button to "Quick Release" the steam, until the valve button drops.
Meanwhile, in a medium bowl mix the mayonnaise, Thai sweet chili sauce, lime juice, and Sriracha together.
Unlock the lid and stir the sauce into the pasta. Let the sauce simmer and thicken 2-3 minutes if needed. Pour in the shrimp and scallions, then mix to combine. Set the Instant Pot on "Sauté" and cook for 2-3 minutes, toss and simmer until the shrimp are pink. Taste, then salt and pepper as needed. Add more Sriracha if desired. Serve warm.
STOVETOP INSTRUCTIONS: Boil the pasta as directed on the package and drain in a colander, reserving 1 cup pasta water. Place the coconut oil, garlic, bang bang sauce (step 2,) and shrimp in the empty pot. Set over medium heat. Pour the pasta into the sauce and toss to coat. Cook until the shrimp are pink. If needed, add some of the reserved pasta water to loosen the sauce.