Preheat the oven to 350°F. Slice each pepper in half lengthwise and remove the seeds. Place them into a glass dish or pan. Cook the orzo according to the package instructions.
Chop the onion, mushrooms, cherry tomatoes, and mince the garlic and herbs. Add the butter to a large skillet over medium heat and add the chopped red and white onions. Sauté until just browning and translucent, about 3-4 minutes.
Drop the bison into the same skillet and increase the heat to medium-high. Stir constantly with a wooden spoon to break up the bison meat. Add the mushrooms, Worcestershire sauce, mustard, garlic, thyme, oregano, red pepper flakes, paprika, and coriander.
Once the bison is no longer red, add the tomato paste and stir to combine. Then pour in the tomato sauce, cooked orzo, and cherry tomatoes. Stir well to combine and bring to a boil.
When the bison mixture is heated through, spoon it generously into each halved pepper and use the excess filling between each pepper. Sprinkle on half of each cheese. Place into the oven for 30 minutes.
Sprinkle on the remaining cheese and broil for an additional 5 minutes or until the cheese is nice and melted.
Serve alongside some simple Mexican corn salad and tortillas for tacos! Enjoy!