Cut 4 (1/4-inch) rings from center portion of bell pepper; set aside. Chop remaining bell pepper. In large microwavable bowl, mix chopped bell pepper, marinara sauce, mozzarella cheese and pepperoni. Microwave uncovered on High 4 minutes, stirring after each minute, until mixture is hot. Divide mixture evenly among ramekins (about 3/4 cup each).