Line an 8x11-inch baking dish (use a 8x8-inch pan for thicker bars) with aluminum foil leaving a 2-inch overhang to use as handles for pulling the bars out with. Spray foil with cooking spray. Set aside. Pour oats and rice cereal into a large mixing bowl. Set aside. In an microwave safe mixing bowl, combine peanut butter, honey, brown sugar, and salt. Heat mixture on high power for 1 minute, remove and stir. Return to microwave and microwave on high power for another minute. Remove from microwave and stir in vanilla. Pour peanut butter mixture over cereal mixture and stir until everything is evenly coated. After the mixture has slightly cooled stir in M&M's. Pour into prepared baking dish and press into an even layer. Cover with plastic wrap and pop into freezer for about 10-15 minutes, or chill in the fridge for about 30 minutes, or until set. Lift bars from pan and cut into bars. Store in an airtight container. Sometimes I wrap each bar individually before placing them in a Ziploc baggie or other container to make them easy to grab and go with. Enjoy!