Preheat oven to 325-degrees. In a large plastic bag with a tight-fitting seal, combine oat squares and pretzels. In a small bowl, stir together melted margarine, brown sugar and cinnamon. Pour over cereal mixture. Seal bag and gently shake mixture until well coated. Transfer to a baking sheet. Bake, uncovered, for 25 minutes, stirring once or twice. Spread mixture onto paper towels to cool. Add marshmallows or fruit and stir to mix. Store at room temperature in an airtight container for up to two weeks.

Microwave Method:  Prepare recipe as directed above except place cereal mixture in a microwave-safe bowl or casserole dish. Microwave on 100% power (high) for three minutes, stirring every minute.