Peel and slice enough potatoes for two people and an onion. Slice the onion in half, then slice each half in thin half moons. Layer the slices of potato and onion in a microwaveable dish, sprinkling each layer with a little salt and pepper.
When you have finished, trickle a little oil on top, a tsp or two. You could add a little grated cheese in the layers or just on top if you like.
Cover the dish and microwave for 5 minutes, this cooks the vegetables. Test they are done with a sharp knife. Undercooked onions are tolerable, undercooked potatoes are pretty unpleasant. Now you just need to brown the top either in the oven if you are using it anyway, or under the grill. The resulting dish is unctuous and delicious.
I sometimes stir in some chutney or fine chopped chillies, or spread out the cooked veg onto an oven tray so there are more crispy bits.
I haven’t tried it yet, but this would work with sweet potato, carrot, swede, turnip or any combination of them or any other root veg that you have. And of course you could use leeks instead of onions, especially if you have any in the garden.