This looks complicated because of all the ingredients but it's very simple to make.
Gado Gado sauce
(about 4 portions)
50g butter
1 large onion, chopped
2 cloves garlic, crushed
1 red chilli
1 tsp grated ginger
150ml peanut butter
2 tsp honey
1 lemon, juice only
300ml water
1 bay leaf
dash tamari or soy sauce
dash cider vinegar
Method
1. Melt the butter
2. Sweat the onion and garlic until soft
3. Add all other ingredients and cook on a low heat for 20 minutes stirring occasionally.
Probably not 100% tradition but I like it with a mix of cooked/uncooked (for a bit of crunch) veggies and fruit (makes it seem more "tropical"). Also I like it to be colourful.
Roasted peeled red pepper, new potatoes (cooked and quartered), cooked French beans, cabbage, raw bean sprouts, cucumber slices, wedges of tomatoes, carrots julienned, sliced avocado, sliced green mango. Whatever you fancy.
You can put everything on a bed of lettuce or use lettuce leaves as a wrap. Iceberg works best for this.
You can buy gado gado "dressing" from Indonesian grocery store. The one that my mother used to buy (she was born in Indonesia) is in brick form and you need to dissolve it in warm water to make the dressing.
If you want to try real authentic Indonesian gado gado, there's a restaurant on Connaught Road Central, just opposite Shun Tak (the ferry terminal to Macau). Their satay is also pretty good. It's the one of the few Indonesian restaurants my mother is willing to dine in in Hong Kong. The other one is located near the Indonesian embassy.