Preheat oven to 475 degrees.: When you turn the oven to 475 degrees , you should hear the faint click and then feel warmth when you open the door after a few minutes, the intense heat helps melt the provolone cheese quickly without overcooking the filling. This oven temperature is important because a hot environment softens the bread interior and loosens the cheese into a glossy blanket, creating a cohesive bite. A common mistake is preheating too low, which can leave the cheese unmelted and the roll soggy, so give the oven time to reach full heat before inserting the sandwiches.
Season chicken with salt, pepper and oregano. In a large skillet add oil, turn to medium-high heat, add chicken and brown on both sides. Add peppers and onions and continue cooking until tender.: As you sprinkle salt, freshly ground black pepper , and the optional oregano over the chicken , you should notice a fragrant herbal and peppery aroma that primes the meat for searing. Properly seasoning now builds layers of flavor that penetrate during cooking, rather than relying on surface seasoning alone. Be mindful not to over salt at this stage if your salt is coarse, taste later and adjust if needed; under seasoned chicken is the more common error.
Place open rolls on a cookie sheet, add cooked chicken, peppers and onions, top off with a cheese slice on each roll. Place rolls in oven and heat until cheese is melted.: As the canola oil heats, it will shimmer on the surface, a signal that the pan is ready. When you add the chicken , listen for the immediate sizzle, and watch for golden brown edges to form, which indicates caramelization and deep flavor development. Flip to brown the opposite side so you get even color, taking care not to crowd the pan, otherwise the meat will steam instead of sear. Overcooking here will cause the chicken to dry out, so aim for a golden crust while keeping the interior juicy.
Add peppers and onions and continue cooking until tender.: When you stir in the sliced red and green bell peppers and the thinly sliced onion , the skillet will fill with sweet, roasted aromas and you may hear a softer sauté sound compared to the initial sear. Cook until the vegetables are tender yet still retain some texture, their sugars will concentrate and complement the savory chicken . Stir periodically to encourage even browning and to infuse the vegetables with the browned bits from the pan, which add flavor. A typical error is overcooking the vegetables until they become mushy, so test a slice for tenderness while keeping some bite.
Place open rolls on a cookie sheet, add cooked chicken, peppers and onions, top off with a cheese slice on each roll.: When you assemble, the hot filling should steam slightly as it meets the room temperature roll, and placing a slice of provolone cheese on top will create a smooth melting interface between filling and bread. Arrange evenly so each roll receives a similar amount of chicken and vegetables, which ensures balanced flavors. If your filling is cooler than expected, give it a quick return to the pan to warm through; the common misstep is assembling with cold filling which delays cheese melting in the oven.
Place rolls in oven and heat until cheese is melted.: Slide the cookie sheet into the preheated oven and watch for the provolone cheese to soften and spread over the filling, becoming shiny and slightly bubbling at the edges. This should take just a few minutes at 475 degrees , and you can peek through the oven glass to monitor the melt. Remove when the cheese has lost its shape and clings to the filling, as leaving it too long risks drying the chicken and toughening the bread. A common mistake is leaving sandwiches in the oven unattended for too long, which can quickly go from melty to overdone.