In a large skillet cook onion, sweet pepper, and garlic in hot butter over medium heat 5 minutes or until nearly tender. Add pot roast with juices. Bring to boiling; reduce heat. Simmer, covered, about 10 minutes or until pot roast is heated through.
Transfer pot roast to a cutting board; keep warm. Remove vegetables from skillet with a slotted spoon, reserving juices in skillet. Simmer juices until reduced to 1/4 cup, about 5 minutes. Cut pot roast into bite-size pieces. Divide basil leaves and pot roast among bun bottoms. Top with vegetable mixture and some of the juices. Spread Basil Mayonnaise on bun tops. Replace bun tops. Makes 4 sandwiches.
In a small bowl stir together light mayonnaise or salad dressing, snipped fresh basil and a dash freshly ground black pepper.