Preheat the grill on high heat.
Cook the garlic: In a medium pan, heat 1 tablespoon of the olive oil over medium heat. When it gets hot, add the garlic and ginger. Season lightly with salt and cook, stirring constantly, until they turn golden brown, 1 to 2 minutes. Remove them from the pan and immediately transfer to a medium bowl to cool. Stir in the pine nuts.
In a larger bowl, combine the remaining 2 tablespoons olive oil with the cucumbers and chili flakes. Toss to coat them with the oil. Season them lightly with salt. Sprinkle them with the sugar, vinegar and the sliced scallions and toss to blend. Combine with the garlic and pine nuts.
Cook the clams and finish the dish: Scatter the clams on the grill in a single layer. Have a pair of tongs and a large platter ready. Clams will being to open after 3 minutes and should take about 10 minutes total. As they open, use the tongs to remove them from the grill and place them on the platter. When they are all opened, squeeze the juice from the lemons over them and scatter the cucumber and pine nuts all around. Try to get the mixture inside the clam shells as well. It's so delicious when you bite into the clam and get all the other flavors (and the char on the outside of the shells) all at once. Serve immediately.