Hi nigelslaterfan,
Here's a link to the recipe page for Mary McCartney's - black bean burgers
And here's what it says:
Ingredients
400g tin of black beans, drained
2 tablespoons of light olive oil
1 medium red onion, finely chopped
140g mushrooms, finely chopped
1 clove garlic, finely chopped
2 tablespoons soy sauce
2 tablespoons mixed herbs
1 spring onion, finely chopped
Half a teaspoon of chilli flakes
1 tablespoon of nutritional yeast flakes (or Marmite!)
Black pepper to taste
Extra oil for frying, if necessary
Method
Heat your oil in the frying pan, then add chopped onion and allow to cook for two minutes. Add in your mushrooms, soy sauce and simmer for 2-3 minutes until all the liquid from the mushrooms has evaporated. Follow this with your garlic, chopped spring onion, herbs, and black beans (slightly mashed up) - and allow to heat through for a couple minutes.
Transfer the mixture into a bowl to cool, then add four tablespoons of flour, a teaspoon of marmite, and a pinch of black pepper to taste.
Shape the mixture into 4-6 burgers, depending on how big you'd like them.
If you're doing these on the BBQ, you'll need to firm them up in the fridge (or even freezer!) for up to an hour beforehand, so they don't fall through the grill! But if you're eating indoors, just pop them into a hot frying pan and cook on both sides for a couple of minutes, until they're browned and heated through.
Serve 'em up either with rice and salad or with all the trimmings of a traditional burger - mayo, ketchup, mustard (you name it!) plus red onion, tomato, cheese and gherkins in a floury bun.
Enjoy! 
By the way, there are plenty of other delicious recipes to be found here