To make salsa: With a sharp knife, remove skin and white pith from oranges and discard. Working over a bowl, cut orange segments from their surrounding membranes. Stir in onion, lime juice, cilantro, jalapeno and garlic. Season with salt and pepper.
To make chicken: Heat a small skillet over medium heat. Add coriander, cumin and pepper; toast, stirring constantly, until aromatic, about 45 seconds. Transfer to a small bowl and add salt.
Preheat grill or broiler.
Coat the chicken with the spice mixture. Grill or broil on a lightly oiled rack until the chicken is opaque in the center, 4 to 5 minutes per side. Top with the salsa.
Make Ahead Tip: The salsa (Step 1) will keep, covered, in the refrigerator for up to 8 hours.