Make citrus vinaigrette by combining all the ingredients in a jar or a tight-sealing plastic container. Shake to blend.
Make salsa by combining mango, red onion, chile, bell pepper, and cilantro with 2 tablespoons of the vinaigrette. Very gently, lightly mix in the avocado into the mango mixture. Drizzle with one more tablespoon of vinaigrette, then cover and refrigerate until ready to serve.
Brush opah with olive oil and add salt and pepper to taste, put on preheated grill, cook 6-8 minutes per side, being careful not to overcook.
Or, preheat oven to 375. Season fish with salt and pepper. Heat a non-stick pan with olive oil, and sear all sides of the opah. When all sides have a nice golden brown hue, place pan in heated oven for a few minutes to finish.
Place salad greens and toasted pine nuts in bowl and toss with remaining vinaigrette. Place a mound of salad on each serving plate. Place fish on top the salad then top with mango-avocado salsa. Drizzle any additional vinaigrette around the plate.