Scale and gut the sardines (you can have your fishmonger do this). Wash the sardines under cold, running water and pat dry with paper towels. Lightly salt the sardines with coarse sea salt and refrigerate. Meanwhile, boil 2 potatoes until a knife is easily inserted. Drain and cool.
Roast 2 red bell peppers over an open flame until charred. Place in a bowl and cover it with plastic to allow it to steam for approximately 20 minutes. Remove the plastic and peel and seed the peppers.
Cut peppers into 3-inch wide strips and combine in bowl with 1/4 cup of olive oil, 1/8 cup white wine vinegar, onion, and garlic. Season with salt and pepper, to taste.
Preheat a grill.
Place the sardines on a hot grill. Cut potatoes in half lengthwise and place on the grill. When the sardines are done on first side, flip them over, and give the potatoes a quarter turn to create the grill marks.
Place 3 sardines on each plate with 2 potato halves and some red pepper salad. For decoration and extra flavor, sprinkle with some thinly sliced onions and garlic over the sardines and drizzle with remaining olive oil.
The ideal accompaniment for this dish is some Portuguese rolls and a nicely chilled Vinho Verde Portuguese wine.