How to Make It
Preheat grill to medium-high heat.
Combine oil, onion, 1/2 teaspoon salt, and garlic in a medium stainless steel skillet. Place skillet on grill; cover and grill 10 minutes or until garlic is soft and golden brown. Remove pan from grill; stir in parsley and juice. Return pan to the grill; cover and grill 2 minutes.
Add shrimp to grill rack coated with cooking spray; grill 4 minutes or until grill marks appear, turning after 2 minutes. Remove shrimp from grill, and place in pan; toss to coat with juice mixture. Sprinkle with remaining 1/4 teaspoon salt and pepper.
Arrange shrimp and mojo on a platter; sprinkle with serrano slices.