Add water to a Dutch oven to a depth of 1 inch; bring to a simmer.
Place chicken in a vegetable steamer.
Place steamer in pan over water; cover. Reduce heat to medium-low. Steam, covered, 10 minutes.
Remove chicken from steamer; cool. Pat dry.
Heat a large skillet over medium-high heat.
Add oil; swirl to coat.
Add chicken to pan; saut 5 minutes, turning to brown on all sides.
Add cilantro and sliced serrano chiles to pan; saut 30 seconds, stirring constantly.
Remove pan from heat; transfer chicken mixture to a large bowl using a slotted spoon.
Bring mango nectar to a boil in a small saucepan over medium heat. Simmer 15 minutes or until reduced to 1/4 cup, stirring occasionally. Stir in lime juice and kosher salt.