A small shop to visit when you come to Senayan City is to try some foods at Okirobox. It is located in food court, in the middle of the court. I tried it several months ago, just remember to post it now.
First thing, don't expect you will be full by eating Okirobox foods. All items should be categorized as snack or side-dishes (although prices are not). You know, japanese foods tend to satisfy eyes and tongue, not stomach.
Takoyaki (Octopus balls)
This snack is made of some eggs I believe, can be filled with Squid / octopus or other meats as you like. One box contains 4 ball. Prices vary from IDR 14,000 to 20,000 per box. Try it and you may like it. Taste sweet and yummy with mayo cream and salmon fish filament topping, unfortunately only 4 balls per serving. By googling a bit, I found how to make takoyaki from here.
Pizza in Japanese version. Unlike Italian rounded version, Okonomiyaki comes in small square size. You can order black-pepper beef, fish, and also octopus okonomiyaki. Similar taste to takoyaki because uses same topping. Its price a bit expensive, range above IDR 20,000, but you have to try it.
PS: Don't forget to ask their staff to add more toppings!