Preheat oven to 350.
Line a baking sheet with foil and grease with cooking spray.
Transfer cut peppers to prepared baking sheet.
Sprinkle the insides with salt; set aside.
Heat olive oil in a large skillet and add the bacon, mushrooms, and onions.
Season with salt and pepper and cook over medium-high heat, stirring frequently, for 8 to 10 minutes, or until tender.
Remove from heat and stir in parsley.
Spoon the mixture into the prepared peppers.
Sprinkle with crumbled feta cheese.
Drizzle with olive oil.
Bake for 35 minutes, or until peppers are fork-tender.