Preheat oven to 350 degrees. Cut peppers in half, scrape out the seeds, carefully remove the membrane with a knife, remove stems and rinse with cold water. Pat dry. Cut the halves in half (cutting the peppers into quarters). Turn upside down on a paper-towel lined plate for about 5 minutes to let any excess fluid drip out.
On a baking sheet lined with aluminum foil and lightly sprayed with non-stick cooking spray, place the peppers, cut side up, in the oven and bake for 20 minutes.
While the peppers are baking, saute the onions and mushrooms on medium high heat in a small skillet with about 4 tablespoons of butter. Once the onions are soft and translucent, remove from heat and let cool.
Combine the ricotta, mozzarella, bacon, onions and mushrooms in a small bowl. Stuff the peppers with the cheese mixture and gently sprinkle more garlic salt and Italian seasoning over the peppers.
Bake for approximately 5-10 minutes, or until cheese has melted. Drizzle with balsamic vinaigrette dressing and freshly grated Asiago cheese, if desired.