Peel the shrimp and use the shells to make your stock.
Combine the seasoning mix ingredients in small bowl.
Combine the onions, bell peppers, and chile peppers; then divide them in half.
Place half these vegetables in a small bowl near your stove so you can add them quickly in the next step.
Heat the oil in a heavy 5-quart pot over high heat until it is smoking hot (500°), about 5 minutes.
Make a roux—add the flour and whisk constantly, making sure that the oil and flour are thoroughly combined, until the roux is a caramel color, about 2 minutes.
When making a roux, it is very important to keep stirring at all times and to keep all of the flour moving. (If you don't, the flour will burn and the roux will be very bitter—useless. If you see little black specks in the roux, it has burned. If this happens, throw it out, clean the pot and begin again. If your roux seems to be browning too fast, take it off the stove and continue to whisk until it has cooled slightly, then return it to the heat.).
As soon as the roux is a caramel color, quickly add the combined onions and peppers, and 3 tablespoons of the seasoning mix.
Keep whisking constantly for about 15 seconds, then remove the pot from the heat and continue to whisk until the roux has cooled down slightly, about 2 minutes. (The roux will continue to darken to a deep brown as you whisk.).
Return the pot to high heat, add the plantains and stir well to mix them with the roux.
Cook, stirring frequently, until the plantains take on a slightly darker color, about 4 to 5 minutes.
Carefully add 4 cups of stock and bring to a boil, whisking frequently and well to dissolve the roux.
At this point the liquid will have a yellowish-brown color and a soft seafood taste.
When the mixture boils, scrape the bottom well, then add the remaining vegetables, the remaining seasoning mix, and the remaining 3 cups of stock.
Cover and return to a boil, then reduce the heat to medium and simmer, uncovering and stirring every few minutes, until the plantains are soft and breaking into smaller pieces, about 12 minutes.
Whisk in the mango purée, re-cover, increase the heat to high and bring to a full boil.
Uncover and add the shrimp, re-cover, and bring back to a full boil.
Cook just until the shrimp are pink, opaque, and plump, about 1 to 2 minutes.
Stir in the parsley, remove from the heat immediately and serve over rice.