Anyone who knows Bangkok's food scene will almost certainly be familiar with Soi Polo Fried Chicken. It enjoys almost legendary status for its whole deep-fried chickens.
KFC could learn plenty of lessons from Soi Polo Fried Chicken. The 50-year-old third generation eatery has perfected the art of gai tod - golden skin and tender, succulent meat without being oily (like much of Bangkok's fried chicken can be). Fistfuls of crispy fried garlic are tossed over the top. Interestingly, though fried chicken is a southern Thai speciality, the rest of the menu is North Eastern Isaan food - som tam papaya salads, meaty larb and grilled catfish.
I'm stretching the idea of street food with Soi Polo Fried Chicken. It's a large quite modern eatery split in half - one side is open-fronted and other is boxed in and air conditioned. Both spaces are utilitarian and while it's a perfectly pleasant place to eat it's not somewhere you visit for the atmosphere.
A whole fried chicken at Soi Polo (good for two as dinner or four as part of a larger meal) is 260 THB (US $8.35). Most of the other dishes hover around the 60-120 THB mark (US. $1.93-3.85), though there are a few expensive exceptions.
Lumphini Park just next door makes for a scenic place to work off your lunch.