Preheat your oven to 400 degrees.
Scoop out the stem and fins from the portabello mushrooms using a spoon- save the mushroom bits for the stuffing.
Dice the onion, green pepper, tomato and mushroom bits and saute in a non stick pan.
There is enough moisture from the vegetables that oil is unnecessary- crumble the the sausage meat (skin removed) into the pan at the same time- stirr in the garlic powder and salt and pepper to desired taste.
When the onions are opaque (approximately 15 mins) pour the spaghetti sauce in, stirr to combine evenly and put in the grated cheddar cheese, once again stirr to disburse evenly and remove from the heat.
Let the mixture rest for approximately 10 minutes to allow the cheese to melt.
Place your mushrooms in an appropriate baking pan or sheet-stuff the mushrooms with the vegetable mixture and sprinkle the top with the grated parmason cheese.
Bake in the oven for 20- 25 minutes or until the parmason cheese is golden in color.
Remove from the oven and let the mushrooms rest for approximatey 5 minutes and serve.