Melt butter in skillet; cook green peppers in butter for 5 minutes or until crisp-tender.
Drain pineapple, reserve syrup.
Add 1 cup reserved syrup, pineapple, onions and bouillon cube to green peppers; bring to a boil.
Reduce heat; simmer for 5 minutes.
Drain and halve cherries.
Drain tuna; break into pieces.
Add tuna, cherries, sugar and vinegar to green pepper mixture; blend well.
Blend remaining reserved pineapple syrup with cornstarch; stir into tuna mixture.
Simmer, stirring constantly, until clear and thickened.
Serve over rice.