Preheat the oven to 400°F Place the shrimp on a large baking sheet with sides. In a small bowl, combine the shallot, lemon zest and juice, olive oil and seasoning salt, and mix to combine. Pour over the shrimp and move them around to evenly coat. Make sure the shrimp are arranged in one layer.
Roast the shrimp for about 8 to 9 minutes, or until they are pink and opaque all the way through. Place in another dish and cool. Refrigerate until serving.
While the shrimp are cooking, prepare the sauce: In a food processor puree the mango. Combine the remaining ingredients together in the food processor and blend until combined. Taste for seasoning. Place in a small serving bowl and serve with shrimp or crab.
To serve as an appetizer: place the sauce in a small bowl in the center of a 12-inch platter. Arrange the shrimp around the outside of the platter in a pretty pattern. Garnish with the parsley. Make sure to have a small bowl next to the platter to dispose of the tails.
To serve as a first course: Place a couple of tablespoons of the sauce in the center of a martini glass. Sprinkle the parsley on top of the sauce. Arrange the shrimp on the edge of the glass; figure 4 to 5 shrimp per person. Serve immediately.
Advance Preparation: The shrimp and sauce can be made up to 1 day ahead, covered and refrigerated.