Grease bottom and sides of an 8” square pan with butter or cooking spray. Place cereal in a resealable food-storage plastic bag; seal bag and slightly crush cereal with rolling pin or the flat side of a meat mallet.
In a large bowl, mix cereal and sunflower nuts; set aside.
In a 3-quart saucepan, heat honey, brown sugar, apples and cinnamon just to boiling over medium-high heat, stirring occasionally. Remove from heat; stir in peanut butter. Pour over cereal mixture; stir gently until evenly coated.
Press mixture evenly into pan with back of wooden spoon. Refrigerate about 1 hour or until set. Cut into 4 rows by 4 rows (16 pieces). Store covered at room temperature.