For the chutney: Blend the cilantro, lemon juice, garlic, ginger, chiles, coconut, pistachios, and cumin in a food processor to a puree.
Heat a small amount of the vegetable oil in a small saucepan over a medium heat. When the oil is hot, add the mustard seeds. Be careful of the popping mustard seeds and splattering of oil. When the mustard seeds start to pop, remove the pan from the heat, and add the seeds to the chutney mixture. Season the mixture well with salt, and freshly ground black pepper.
In a separate bowl, mix 2 tablespoons of the chutney mixture with 1 tablespoon vegetable oil. Brush the chutney mixture all over the sea bass, and set aside to marinate for 20 to 30 minutes.
While the fish is marinating, preheat the oven to 350 degrees F.
When the fish has marinated, spoon the remaining chutney mixture into the cavities of the sea bass. Place the stuffed sea bass onto a sheet pan, and bake in the oven for 15 to 20 minutes, or until the flesh of each sea bass is opaque.
To serve the dish, divide the stuffed sea bass among four serving plates. Spoon a portion of the new potatoes and green salad alongside. Garnish each plate with a wedge of lemon.
Adding pistachios to the chutney helps to bind it and the nuts absorb the juices that leak into it from the fish. You can also use peanuts as a substitute for the pistachios.