Preheat oven to 400 degrees.

Using an ovenproof skillet large enough to hold the four chicken breasts, heat 1 tablespoon olive oil in a heavy skillet over medium-high heat. Sauté onion, celery & bell pepper for several minutes, until just starting to soften and the onion is translucent. Remove from vegetables from skillet and set aside.

While the vegetables are cooking, slice chicken breasts horizontally, from the thick side towards the edge, making sure to keep them intact. Open like a book: to make them lay flat, make a few shallow slices, being careful not to slice through, in the thickest part of the breast. Using a meat pounder, gently pound out to about 3/8ths inch thick.

Divide the cheese among the four breasts, leaving 1/2 inch border around the outside edges. Divide vegetable mixture in the same way on top of the cheese. Roll up and secure with toothpicks, weaving them through the long way. Season generously with Cajun seasoning and rub in.

Heat the remaining olive oil and add the chicken breasts, seam side up, partially turning so nicely browned across the tops and sides. Turn over and place in oven for about 20 minutes until a thermometer registers 165 degrees.

Rest for a few minutes and slice into medallions if desired or serve whole. Sprinkle with green onion if desired.

Note: If you’d like this cheesier, mix grated cheese with about 2 ounces of room temperature cream cheese, then spread the mixture on the breasts.