For the green onion dressing:
Heat a grill. Drizzle 1/2 teaspoon of olive oil over the white portion of the green onions. Place the white bottoms of the green onions on the hot grill and grill until they are slightly softened and charred. Put the grilled whites of the green onions, the green onion tops, garlic, white wine vinegar, Dijon mustard and remaining olive oil in a blender, puree until smooth. Transfer the mixture to a bowl and stir in the sour cream. Season the dressing with salt, and black pepper, to taste. Set the dressing aside.
For the pasta salad:
Heat a grill. Place the cooked pasta in a large bowl, toss with 2 teaspoons of vegetable oil. Drizzle the remaining 1 teaspoon of vegetable oil over the red onion rings and season with salt.
Place the red onions on the hot grill and grill until softened, approximately 10 minutes, remove the onions from the grill. Coarsely dice the grilled red onions. Add the chopped red onions, red pepper, yellow pepper, orange pepper, chopped parsley, and green onion dressing to the pasta. Mix to incorporate all ingredients. Season the pasta with salt, and pepper, to taste. Garnish with toasted coconut.