Preheat the oven to 130 ̊C, gas mark 1⁄2. To make the muesli, gently heat together the oil, honey, maple syrup, vanilla and cinnamon in a small pan over a low heat for 2–3 minutes, stirring to combine. In a large bowl, mix together the oats, wheatgerm, coconut, nuts and seeds. Pour the syrup mixture over the top and mix together until evenly coated.
Spread the mixture evenly over a flat baking tray and bake for 40–45 minutes, stirring regularly, until golden and dry. Allow to cool completely on the tray, then stir through the raisins and dates. The toasted muesli will keep in an airtight container for 4 weeks.
Turn the oven up to 150 ̊C, gas mark 2. Toss the rhubarb with the sugar, orange zest and juice and place in a single layer in a roasting tin. Cover the tin with foil and bake for 30–35 minutes, until just soft.
Serve the muesli with the baked rhubarb and Greek yogurt.