Preheat the oven to 350°F and line a baking sheet with parchment paper. Cut the peppers in half lengthways. Scoop out the seeds and arrange the peppers on the baking sheet.
In a bowl, mix the Boursin cheese with the garlic, half the Gruyère, and the green onion.
Use a teaspoon to scoop the cheese mix and fill the peppers.
Sprinkle the rest of the shredded Gruyère over the peppers. Bake in the oven for 15 minutes or until the cheese is bubbly and golden brown.