Preheat the oven to 200°C/400°F. Put the oats into a bowl and sprinkle over the cinnamon and vanilla extract, tossing to coat evenly, then spread them out on a baking sheet.
On a separate baking sheet, sprinkle over the flaked almonds, sunflower seeds, pumpkin seeds and hazelnuts and place on the top shelf of the oven with the porridge oats underneath. Bake for 10–15 minutes until lightly toasted, tossing occasionally so that they cook evenly. Remove from the oven and leave to cool.
Once cool, place the toasted porridge oats, nuts and seeds in a large bowl. Stir in the wheat germ with the cranberries, coconut, banana chips, raisins and linseed, if using. Transfer to a 1.2 litre Kilner jar or airtight container and seal tightly with a lid. It will keep for up to 2 weeks.
To serve, weigh a 50g portion of the muesli into a bowl and scatter the blueberries, sliced banana, strawberries and/or grapes on top to garnish. Pour over the milk or add a dollop of yoghurt.