1. Preheat your oven to 375 F (190 C). Wash the bell peppers thoroughly. Carefully slice each pepper in half lengthwise, from stem to tip. Use a spoon to scoop out and discard the seeds and any white membranes inside. Place the pepper halves cut-side up in a baking dish.

2. Heat the olive oil in a large skillet over medium-high heat. Add the ground beef and break it apart with a spoon. Cook, stirring occasionally, until the meat is fully browned and no pink remains, typically about 5-7 minutes. Drain any excess grease from the skillet.

3. Reduce the heat to medium. Sprinkle the taco seasoning mix over the browned ground beef. Pour in the 1/2 cup of water. Stir everything together well, ensuring the seasoning is evenly distributed. Bring the mixture to a simmer and cook for 2-3 minutes, or until the liquid has mostly evaporated and the meat is well-coated with the seasoning.

4. Remove the skillet from the heat. Stir in half of the shredded cheddar cheese and half of the shredded Monterey Jack cheese into the seasoned ground beef mixture. Mix until the cheese is just melted and incorporated. Carefully spoon this cheesy taco meat mixture evenly into each of the prepared bell pepper halves, mounding it slightly if needed.

5. Sprinkle the remaining shredded cheddar cheese and Monterey Jack cheese generously over the top of each filled bell pepper.

6. Place the baking dish with the stuffed peppers into the preheated oven. Bake for 20-25 minutes, or until the bell peppers are tender-crisp and the cheese on top is melted, bubbly, and lightly golden brown. If you prefer softer peppers, you can bake them for an additional 5-10 minutes.

7. Carefully remove the baking dish from the oven. Let the stuffed peppers cool for a few minutes before serving, as the filling will be very hot. Garnish with chopped green onions, if desired, and serve with optional sour cream or salsa on the side.