Pork Lettuce Wraps with Grapefruit

Name: Pork Lettuce Wraps with Grapefruit
Ingredients: 2 tablespoons fish sauce; 2 tablespoons fresh lime juice; 2 teaspoons packed dark brown sugar; 3 tablespoons shredded unsweetened coconut; 1 medium pink grapefruit; 3 tablespoons chopped roasted salted peanuts; 1/2 cup coarsely chopped fresh mint; 1 teaspoon hot Asian chili sauce (sambal oelek or sriracha); 2 scallions, thinly sliced diagonally; 2 tablespoons vegetable oil; 1/2 pound lean ground pork; 1 teaspoon finely grated peeled ginger; 1 small red onion, halved and thinly sliced; Romaine or Bibb lettuce leaves, for wrapping