Preheat oven to 350 degrees.
Cut tops off of peppers, and remove the inside; keep the top portion of the pepper, to cover while baking.
If rice is not cooked yet, follow instructions on package and do this now.
Heat a medium size skillet over medium heat; drizzle oil into skillet, add onions and minced garlic. Saute for 1 mintue.
Add tomato sauce, beans, seasonings and rice; combine thoroughly.
Place an even amount of mixture into each pepper, place top of pepper on top; sprinkle with cheese, and lightly cover peppers with foil.
Bake for 35-40 minutes; until peppers are softened. Top with yogurt and salsa if desired.
Cut watermelon into cubes and serve on the side.