Combine first 7 ingredients in a small saucepan; cook over medium heat 2 to 3 minutes or until sugar dissolves. Pour half of soy sauce mixture (about 1/2 cup) into a small bowl; set aside to cool.
Bring remaining soy sauce mixture to a boil over medium heat; reduce heat, and simmer 9 to 11 minutes or until mixture is reduced by half and forms a thin syrup (about 1/4 cup). Remove from heat, pour into a small bowl, and refrigerate until ready to serve.
Pour reserved 1/2 cup soy sauce mixture into a zip-top plastic bag. Add fish and bell peppers; seal bag and marinate in refrigerator 1 hour, turning occasionally.
Remove fish and bell peppers from marinade; discard marinade. Thread fish, bell pepper, and pineapple alternately onto 6 (12-inch) skewers.
Place on grill rack coated with cooking spray; grill 3 to 4 minutes on each side or until fish is opaque. Remove from heat; brush with reserved soy sauce mixture.
Note: If you use wooden skewers, be sure to soak them in water for 30 minutes to prevent the wood from burning on the grill.