Preheat the oven to 450F.
In a small bowl, combine the cream cheese, sour cream, and onion powder. Whip well until free from lumps and well combined.
Fold in the shredded cheese.
Use a teaspoon to scoop the cream cheese mixture into the split mini rainbow peppers, using the back of the spoon to level off the cream cheese.
Once all of the mini peppers are filled and no cream cheese mixture remains, place the stuffed mini rainbow peppers in a large cast iron skillet, or on a parchment lined sheet pan.
Bake in the oven for 15 minutes, or until bubbly and the cheese is melted.
Sprinkle the stuffed peppers with your minced green onion and serve immediately.