Preheat oven to 180C. Grease and line the base and long sides of a 19 x 29cm slice pan.
Combine the honey, sugar and butter in a saucepan over medium heat. Cook, stirring, for 5 minutes or until butter melts and sugar dissolves.
Bring to the boil and cook for 2 minutes or until syrup thickens slightly.
Remove from heat. Combine the muesli, sultanas, sunflower seeds, pumpkin seeds and cinnamon in a large bowl.
Pour over the hot syrup and stir to combine.
Spoon into pan and press gently with the back of a spoon.
Bake in oven for 30 minutes or until golden brown and crisp. Remove from oven and set aside in the pan to cool completely. Cut into 5cm x 9cm rectangles to serve.