Preheat oven to 350°F. Cut the tops off the peppers and remove the seeds and membranes from the insides.
In a large bowl, gently mix together the remaining ingredients. Stuff each pepper with ¼ of the mixture.
Place the stuffed peppers in a 8x8 inch casserole dish. Pour ¼ cup water in the bottom of the dish.
Cover and bake for 45 minutes. Uncover and bake for an additional 15 minutes.
Serve immediately.
Notes
You can chop the tops of the peppers (that you cut off) and add them to the mixture, if you'd like. Substitute ground turkey (dark meat preferably, so it doesn't dry out) in place of the ground beef. Make it ahead: prepare and stuff the peppers but do not bake. Cover and refrigerate for up to 24 hours. Bake according to written directions. The baked peppers can be frozen for up to 2 months. Wrap in foil and place in a freezer bag. Defrost for 24 hours in the refrigerator before reheating.