Sauté the onions in a large non-stick frying pan for 3-5 minutes, or until translucent. Add the mince and cook for 5-7 minutes, or until browned.
Add the beef stock, diced tomatoes, and carrot/zucchini, and simmer for 15-20 minutes, or until slightly thickened.
In a separate frying pan, melt the butter, then add the flour. Whisk together until combined. Remove from heat and gradually add the chicken stock, continuously stirring to remove any lumps.
Assemble the lasagnes in 4 individual portions, layering meat sauce, lasagne sheet and white sauce. Repeat the layers as needed.
Finish each portion with shredded cheese. Allow to cool before freezing.
Remove the frozen individual lasagne portion from the freezer and place it in an oven-safe dish, or leave it in the container if it is suitable for oven use.
Cover loosely with foil. Bake from frozen at 180°C (350°F) for approximately 40-45 minutes, or until heated through and bubbling around the edges.
Remove the foil for the final 5-10 minutes of cooking to allow the cheese to melt and become golden. Enjoy!