Preheat your oven to 375°F and line a baking sheet with parchment paper for easy cleanup.
In a large skillet over medium heat, cook the sausage until browned and crumbly, about 6-8 minutes. Drain any excess grease and let it cool slightly.
In a mixing bowl, combine the cooked sausage, cream cheese, mozzarella, Parmesan, garlic, red pepper flakes, and oregano. Mix until everything is well combined.
Arrange the pepper halves on your prepared baking sheet, cut side up.
Spoon the sausage mixture generously into each pepper half, mounding it slightly.
Sprinkle the panko breadcrumbs over the top of each stuffed pepper for a nice golden crunch.
Bake for 20-25 minutes until the peppers are tender and the tops are golden brown.
Let them cool for 5 minutes, then garnish with fresh parsley before serving warm.