I tweaked the ingredients a little based on what I have in the fridge. Here's the recipe
Red Onion Relish
adapted from BBC Good Food
Ingredients
juice of 1/2 lemon
4 pickle red chillies (an asian brand-vietnamese specifically) , slice finely
small handful flat-leaf parsley leaves
1 small red onion, cut into wafer-thin slices
a few dashes of fish sauce
1 tsp sugar
freshly milled black pepper
just toss all ingredients together and top it on the hamburger!