In the same pan, pour one can of Mango nectar and simmer on medium low heat until reduced and thickened, about 5 minutes or more depending on the thickness of your canned nectar.
Meanwhile peel the mangoes and cut into one-inch chunks. Make a circular cut around the mango, top to bottom, following the edge of the mango seed. Then cut one-inch slices across the grain on both flat sides of the seed. With a long knife, cut your chunks away from the seed.
Add shrimp to the mango reduction and simmer until they turn pink and opaque.
A good way to test a reduction sauce is to pull a flat edged spatula across the pan. If the sauce holds back for an instant, as shown here, you have a nice not-too-thick-not-too-thin reduction.
Set the shrimp and sauce aside in a bowl to cool down a bit.
Then carefully fold in your mango, plantains and cilantro. Serve warm or "boat" temperature.