I make extra portions of things like cottage pie, homemade meatballs in sauce and lasagne at home and freeze them in foil takeaway trays so we have a meal or two we can take with us and heat up quickly while getting pitched on the first night or if we have a day out and about.
Thai green curry is easy and quick to do in the van - just stir fry some chicken, onion and peppers or whatever veg you like add a spoon or two of curry paste and a tin of coconut milk (light version if preferred) and simmer till cooked through, serve up with a packet of microwavable coconut or jasmine rice - only one pan to wash then

Cous cous is another favourite of mine - just add boiling water and its done - nice with grilled chicked or salmon (wrap in foil with a squeeze of lemon juice and a few herbs if you have them and stick in oven for about 10-12 mins) and a bit of salad.
We recently invested in a Cadac so have done cooked breakfasts, pancakes, steak and jacket wedges, burgers, chicken etc on that.
You can do anything you would at home really but I prefer to keep to quick and simple dishes as I don't want to be a slave to cooking while on holiday !