Preheat oven to 375*, 10 minutes before cooking. Heat oil in a skillet and cook the green onions and pepper until soft. Remove from the skillet with a slotted draining spoon and place in a large bowl.
Drain the tuna, then stir into the green onions and pepper. Beat the ricotta cheese with the lemon zest and juice and the sniped chives until soft and blended. Season to taste with salt and pepper, add the tuna and mix together. If the mixture is still a little stiff, add a little extra lemon juice.
With a teaspoon, carefully spoon the mixtures into the cannelloni tubes, then lay the filled tubes in a lightly oiled shallow ovenproof dish. Beat the egg, cottage cheese, plain yogurt, and nutmeg together and pour over the cannelloni. Sprinkle with the grated mozzarella cheese and bake in the pre-heated oven for 15-20 minutes, or until the topping is golden brown and bubbling. Serve immediately.