Preheat oven to 180°C/160°C fan-forced. Place the lasagne sheets on a microwave- safe plate. Microwave on HIGH (100%) for 1 minute. Microwaving the fresh lasagne sheets helps to separate them more easily before using.

Combine tuna, peas and lemon juice in a bowl. Set aside.

Make Creamy white sauce: Melt butter in a saucepan over medium-high heat. Add flour. Cook, stirring, for 2 minutes or until mixture is bubbling. Gradually stir in milk. Cook, stirring, for 5 minutes or until sauce thickens. Remove from heat. Stir in cheddar and parmesan. Season with salt and pepper.

Lightly grease a 6 cup-capacity ovenproof dish. Place 2 lasagne sheets over the base of prepared dish, trimming to fit. Spoon 1⁄4 of the white sauce over sheets, spreading with the back of spoon. Top with 1⁄3 of the tuna mixture. Repeat layers twice more, finishing with remaining lasagne sheets and white sauce. Cover with baking paper, then foil. Bake for 25 minutes or until heated through.

Meanwhile, make Crunchy garlic crumb: Combine all ingredients in a bowl.

Remove foil and paper from lasagne. Sprinkle with crumb mixture. Bake for 10 to 15 minutes or until golden. Stand for 5 minutes. Serve.