Place cleaned clams in a large bowl and drizzle with enough olive oil to coat generously. When grill is hot, arrange clams on grill and cook until shells open, about 5 minutes.
Meanwhile, whisk lemon juice, chives and garlic together in a medium bowl. Slowly whisk in remaining 1/2 cup olive oil until emulsified. Stir in peppers. Season vinaigrette, to taste, with salt and pepper.
When clams have opened, arrange in their shells on a serving platter. Discard any that have not opened. Drizzle with vinaigrette and serve immediately.