How to Make It
Preheat grill to high (450°F to 500°F). While grill preheats, fill a heavy-bottomed pot with water to a depth of 1 inch; bring to a boil over high. Add clams; cover and cook until shells open, 6 to 8 minutes, transferring clams to a baking sheet as they open. Discard any clams that do not open.
Stir together scallions, rau ram, fried shallots, oyster sauce, oil, sugar, and pepper in a small bowl. Remove clam meat from shells, and coarsely chop. Discard top shells. Stir chopped meat into scallion mixture; spoon evenly into bottom shells. (If using mussels, spoon about 2 teaspoons scallion mixture directly onto meat inside each shell, leaving top shells intact.)
Place prepared clams on unoiled grill grates; grill, covered, until scallion mixture bubbles, about 2 minutes. Carefully transfer to a platter; sprinkle evenly with peanuts, and serve.