-Segment the grapefruit. Using a sharp knife, carefully slice the top and bottom from the grapefruit. Slice the peel and white pith from all around the fruit. (Don’t worry if it’s not perfect!) Cut between the membranes to release the grapefruit segments. Slice the segments crosswise into ½-inch pieces and transfer them to a medium bowl. Add the avocado, scallions, half the lime juice, and a tiny pinch of salt to the bowl. Gently toss to combine. Cover tightly with plastic wrap and briefly set aside. (You can also pop this in the refrigerator if making ahead, or if you prefer a chilled topping.)
In a small bowl combine the soy sauce, garlic, sriracha, honey, toasted sesame oil, and the remaining lime juice. Place this mixture by the stove along with an empty medium bowl.
Pat the shrimp dry with paper towels, and chop them into small (roughly ½-inch) pieces.
Heat the light sesame oil in a large nonstick skillet (or wok) over medium-high heat. When the oil is hot and shimmering, add the shrimp in an even layer and cook for about 2 minutes, stirring occasionally, just until lightly pink and turning opaque. Add the sauce and cook for about 2 minutes more, or until the shrimp is cooked through and the sauce has thickened slightly. Immediately transfer the shrimp and sauce to the waiting bowl.
Assemble the lettuce wraps! Add a little bit of shrimp and sauce to each lettuce wrap. (I like to double layer Bibb leaves for extra security.) Top with some of the grapefruit-avocado mixture and sprinkle with peanuts. Serve immediately.