"Peaburgers" is such a terrible name. Think of these as falafel-like patties.
Here's the retro recipe for Peaburgers as seen in the above Batchelors ad.
1 can Batchelors peas
2 teacups brimful stale breadcrumbs
2 level teaspoons salt
1 level teaspoon pepper
1 tablespoon ketchup or piquant sauce
1 level teaspoon mustard
3 tablespoons thick brown gravy
1 egg (optional)
2 tablespoons chopped onions
Chop and fry onions in a little fat and water until soft. Mash peas and mix all ingredients together including onions. With floured hands form into eight shapes. Fry in shallow fat for 10 minutes. Serve with potatoes and gravy.