Prepare your braai and allow coals or wood to burn down, or preheat a gas braai on medium.
In a mixing bowl marinate the mushrooms in olive oil, salt and pepper. Braai on medium heat until cooked through and beginning to turn golden brown.
Place on a wire rack and allow the mushrooms to release any excess liquids as they cool. Once cool cut the mushrooms in half and then slice into 3 mm slices.
In a large mixing bowl combine the cream cheese and shredded cheddar cheese. Mix well until smooth.
Add the chives, onion and garlic powders. Season. Again mix well until homogenous. Add in the mushrooms and mix gently so as not to break the slices.
Spoon in about a tbsp of filling into each half of the jalapenos.
Braai the stuffed jalapenos with the braai lid closed for 10 to 12 min or until the cheese is bubbling and beginning to brown.Allow to cool slightly before serving. Note: for spicier poppers add some of the jalapeno seeds back into the filling.