Start with preparing ground beef. I've written a complete post detailing exactly how to grind meat at home the clean way. I recommend you check that out.
Peel, rinse, and slice mushrooms. Peeling the outer layer of the mushroom is totally optional, but I like my meals prepared in the cleanest way possible, so I peel them in addition to rinsing.
As soon as the water evaporates, add sliced mushrooms and continue sautéing the meat with mushrooms. The mushrooms will release water and that is fine. Cook until the water evaporates again.
Once the water has evaporated, reduce the heat to medium-low and add the mixed seasonings. Combine seasoning with meat and mushrooms and sauté for about 5 minutes, and stir occasionally.
Mix the pizza sauce and tomato paste into the meat and mushroom mixture and let it simmer for 5 minutes, stirring every minute or so. Set aside and let it cool completely before combining it with cheese and greens.
Rinse and clean the bell peppers well. Cut each pepper in half, including the stems. This is optional but it looks prettier. To split the stem in half, cut from the top of the stem down. Remove all the seeds and membranes since they are bitter.
Rinse and clean the bell peppers well. Cut each pepper in half, including the stems. This is optional but it looks prettier. To split the stem in half, cut from the top of the stem down. Remove all the seeds and membranes since they are bitter.
Place halved bell pepper into a large bowl and cover the peppers with hot boiling water. Let the peppers steam in the water for 10 minutes. Drain the water and set it aside to cool until ready for use.
Transfer the cooled meat and mushroom mixture into a large bowl along with the remaining shredded cheese and add the greens. Mix everything together. Add more seasoning (salt and/or pepper) to taste, if necessary.
Preheat the oven to 350 F. Spoon the filling into the bottom of the peppers and fill it properly. Then place them into an oven-safe 9 X 13 baking dish cut side up into the bottom of the baking dish.
Cover the pan with aluminum foil and bake for 45 minutes. If the peppers were made ahead of time and were refrigerated, then it will take approximately 55 minutes instead.