Add the oil to a large frying pan; add the mince, onion and garlic to the frying pan; season with salt and pepper and brown for 6-8 mins
Add the beef stock powder and dried mixed herbs to the mince mixture; stir to coat
Peel and grate the kumara and carrots and add to the frying pan
Thinly slice the silverbeet and add to the frying pan
Add the jar of passata sauce to the frying pan; cover and simmer for 20 mins; stir occasionally and add some water if needed
Cheese Sauce
Add the butter to a saucepan and melt; add the flour and cook with the butter for 1-2 mins. Remove the saucepan from the heat and whisk in the milk. Return the saucepan to the heat and bring to the boil; stir constantly until the sauce thickens. Grate 1 1/2c of cheese and add to the sauce; season with salt and pepper
Assemble the lasagne by layering the mince and vegetable mixture, lasagne sheets and cheese sauce; repeat until all of the mixture has been used up
Grate 1/2c of cheese and sprinkle over the top of the lasagne