Heat oven to 375°F. Spray a foil-lined baking sheet with vegetable cooking spray. Place salmon fillets on prepared baking sheet. Cook in oven until salmon is firm to the touch (about 10 minutes per 1-inch thickness).
Meanwhile, heat oil in a medium saucepan. Add cumin and cook 1 minute. Stir in black beans and corn. Cook to heat through. Stir in cilantro and lime juice.
In a small bowl, combine salsa and butter. Microwave for 1 minute, or until butter melts. Spoon sauce over salmon fillets.