In a 2-quart saucepan, heat the water to boiling over medium-high heat. Stir in the rice. Reduce the heat to low; cover and simmer for 15 minutes or until the liquid is absorbed and the rice is tender.
Preheat the oven to 375℉.
Heat a large skillet over medium-high heat. Cook and stir the beef in the hot skillet until browned and crumbly, 5 to 7 minutes; drain and discard any grease. Mix the taco seasoning into the ground beef. Stir in the beans, tomatoes, 1 cup of the cheese and the cooked rice.
Place the pepper halves cut-side-up in an ungreased 13x9-inch baking dish. Fill each pepper half with the filling, mounding as you can.
Cover tightly with foil; bake 35 to 40 minutes or until the peppers are crisp-tender and the filling is thoroughly heated. Uncover; sprinkle the tops of the peppers with the remaining ½ cup of cheese and the green onion or cilantro. Bake uncovered for 5 minutes longer or until the cheese is melted.
Notes
Don’t overcook peppers—they should be tender but hold shape
Use fire-roasted tomatoes for best flavor
Make ahead friendly—assemble and refrigerate before baking