Lightly spray the bottom of the pot AND the underside of the lid.
Cut the bell peppers in half (as illustrated) and seed them; chop any pepper pieces to fill the pot.
Rinse the rice several times in cool running water; drain well.
Peel and dice the onion. Heat the oil in a large sauté pan. Add the diced onion and cook over medium-low heat, stirring often, until onion is soft and lightly golden.
Add the ground beef, stirring and crumbling, until well mixed and beef is just cooked through. Stir in the rice to combine and continue to cook and stir over medium-low heat just until rice is lightly “toasted”, about 10 minutes.
Remove from heat and mix in the salt, pepper, paprika and cayenne.
Lay the pepper halves in the pot and fill surrounding area with any remaining pepper pieces. Fill the hollows of each pepper with the meat mixture, mounding generously. Fill any open areas surrounding pepper halves with any remaining mixture.
Slowly pour the tomato sauce atop the peppers. Add water to bring the liquid to about 1” above the top of the peppers. Note that additional liquid will need to be added as the peppers cook because the rice will absorb it!
Bring the mixture to a boil over medium-high heat, then immediately drop the temperature to medium-low. Cover the pot.
Cook covered over medium-low heat, for 35 to 45 minutes or until the peppers have softened and the rice is cooked through.