Bring a large pot of lightly salted water to a boil. Cook lasagne in boiling water for 8 to 10 minutes, or until al dente. Drain, rinse with cold water and place on greaseproof paper to cool.
Cook capsicums and onion in olive oil in a large saucepan until onions are translucent. Stir in diced tomatoes, tomato paste, water and chilli flakes. More chilli flakes can be added if spicier sauce is preferred. Simmer for 30 minutes.
Preheat oven to 190 degrees C. In a medium bowl, combine Parmesan cheese, ricotta cheese, mozzarella cheese, eggs, black pepper and oregano.
Place a small amount of sauce in the bottom of a 20x30cm baking dish. Reserve 1/2 cup of the sauce. Place three lasagne sheets lengthways in pan. Layer some of the cheese mixture and the vegetable sauce on top of lasagne. Repeat layering with remaining ingredients, ending with lasagne. Spread reserved sauce over top of lasagne. Sprinkle with grated Parmesan cheese if desired.
Cover dish with foil and bake for 40 minutes or until bubbly. Remove foil during last 10 minutes of baking.