To make filling, place onion and garlic in a non stick frying pan and cook stirring, for 5 minutes or until onion is soft. Add mushrooms and cook, stirring for 3-4 minutes longer. Place ricotta cheese and tuna in bowl and mix to combine. Stir in mushroom mixture and dill.
Cut lasagna sheets in half. Spoon filling down the center of each half sheet and roll up . place roll join side down in a lightly oiled ovenproof dish
To make sauce, melt butter in small saucepan. Stir in flour and cook for 1 minute. Stir in reserved tuna liquid and lemon juice and cook, stirring for 3-4 minutes or until sauce thickness. Remove pan from heat and set aside to cool. Mix in yogurt and season to taste with black pepper.
Pour sauce cannelloni and sprinkle with parmesan cheese bake for 30 minute or until heated through and top is golden.