Preheat oven to 200°C Cook the sweet potato in a saucepan of boiling water for 5 minutes or until tender. Drain.
Meanwhile, spray eight 125ml (1/2-cup) capacity muffin pans with olive oil spray. Line the bases with non-stick baking paper. Combine the egg, milk, tuna, corn, chives, feta and half the parmesan in a bowl. Season with salt and pepper.
Add the sweet potato. Stir gently to combine. Divide the mixture evenly among the prepared pans. Sprinkle with the remaining parmesan. Bake for 18 minutes or until golden and set. Serve with aioli and baby cos lettuce.