Preheat the oven to 325 degrees and grease two large baking pans. Put the oats, sunflower seeds, sesame seeds, walnuts, and cinnamon in a bowl.
Put the sugar, honey, and butter in a pan, and heat, stirring, until the butter has melted.
Pour over the oat mixture in the bowl and mix well.
Put half the mixture in each baking pan, spreading it out and then pressing it into a thin layer. Put both pans in the oven and bake for about 20 minutes. Turn the mixture over with a spoon and return the pans to the oven, the bottom one now on top.
Bake for another 15 to 20 minutes, or until the granola is deep golden, turning it again during this time to give it an even color and break it up slightly.
Take care not to overcook it, as just past perfect can make it bitter.
Turn off the oven and leave it in for another 10 minutes or so, then get it out of the oven, and leave it to cool completely in the pans. Once cool, this keeps very well in a cookie jar or something else airtight.