Place the salmon filets in a zip-top storage bag or a baking dish skin side up.
In a small bowl, add soy sauce, oil, honey, lime juice, garlic, chili powder, chipotle powder, cumin, smoked paprika, and red pepper flakes. Whisk to combine.
Pour the marinade over the salmon, close the bag or cover the baking dish, and marinate in the refrigerator for 1-8 hours.
Transfer the salmon to a plate and set aside.
Pour the marinade into a small saucepan and bring to a boil over high heat. Reduce heat to low and cook for 5 minutes, stirring occasionally, until it has reduced slightly. Remove from heat.
Preheat the grill over medium-high heat (between 375°F-450°F). Apply oil on the flesh side of the fish and the grill grates so that the surface becomes nonstick.
Place the salmon on the grill skin side up, close the grill, and cook for 3 minutes.
Flip the salmon over with a spatula or tongs, brush some of the reduced marinade over each of the filets, then close and cook for another 4 minutes. (The salmon should have an internal temperature of 120-130F.)
Remove the salmon from the grill and serve with mango salsa.
For the mango salsa
Add all ingredients to a small bowl and mix together to combine. Taste and season with more salt if necessary.