
Make the mango salsa. Add the mango, red onion, cucumber, jalapeno pepper, cilantro, lime juice, and salt to a mixing bowl. Stir together until it's combined. Set aside.
Season the salmon. Pat the salmon dry with a paper towel. Coat all sides of the salmon with oil, then season with garlic powder, salt, and pepper.
Grill the salmon. Preheat an outdoor grill or indoor grill pan to high heat. Brush the grates or pan with oil. Place the salmon flesh side down and cook for 3 minutes. If using an outdoor grill, close the lid. Gently flip the salmon over by using a spatula to slide under the salmon (you can also use tongs to carefully assist), and cook for an additional 2 to 5 minutes, depending on the thickness of the filets.
Top with salsa. Remove the salmon from the grill, let it rest for 2 to 3 minutes, then squeeze fresh lemon juice on top. Top with a portion of mango salsa before serving.