- Preheat the grill.
- Put the sweet potato in a pan of boiling water, bring to the boil and simmer for 5 minutes. Add the broccoli and simmer for a further 5 minutes. Drain and return to the pan. Set to one side until needed.
- Heat the oil in a wok and fry the onions and peppers until the onion begins to soften. Add the mushrooms and courgettes until they begin to brown. Add the soy, sweet potatoes and broccoli. Mix together and pour into a large casserole dish.
- Melt the butter in a saucepan and add the flour. Cook for 30 seconds. Add the milk and cheese and bring to the boil, stirring frequently. The sauce should thicken. Season with salt and pepper. Pour over the veggies.
- Put the tortilla chips on top and sprinkle over with cheese. Place under the grill for 2-3 minutes or until the cheese melts and the chips begin to brown.