Cook rice as directed on package. Remove corn from freezer and allow to thaw.
Cut the tops off of the peppers, removing the seeds and ribs from the inside of each. Dice onion; drain and rinse beans.
In a mixing bowl, combine the marinara sauce, beans, corn, onion, rice, spices, and cheese. Mix well.
Stuff as much of the filling as possible into each of the cored peppers. Add the water to the slow cooker and carefully nestle the peppers into the pot.
Cover and cook on low for 5-6 hours or on high for 3-4 hours. The peppers will wilt a bit but should stay intact; be careful not to over-cook or they will be mushy. Carefully remove them with serving spoons.
Top with extra sauce if desired and serve with pineapple chunks on the side.