Heat oven to 425°F. In 10-inch skillet, melt butter over medium-low heat. Cook onion in butter 10 minutes, stirring frequently, or until light golden brown and caramelized. Add bell peppers; cook 5 to 6 minutes, stirring frequently, until peppers are tender.
On ungreased cookie sheet, unroll dough into 1 large rectangle (if using crescent rolls, firmly press perforations to seal). Press into 12x7-inch rectangle, forming 1/4-inch rim around edge of dough. Sprinkle with Italian seasoning and garlic powder; top with half of cheese, pepper mixture and remaining cheese.
Bake 10 to 14 minutes or until edges are golden brown and cheese is melted. Let stand 5 minutes. To serve, cut in half lengthwise, then crosswise into strips. Serve warm.