In a city with a Thai joint seemingly on every corner, true gems can be hard to find. Rainbow, a perky BYO on an unremarkable commercial strip of Western Avenue, is decidedly one of them. Go beyond the well-executed carryout staples—which include a sauce-slicked pad see ew, the wide noodles pan-fried to a light crisp—and delve into the intriguing regional specialties: fermented Isan-style sausages, beef jerky in an umami-rich marinade, a banana blossom salad dressed in a faintly floral coconut milk sauce. These days, plenty of Chicagoans are in on the secret of this place, hence the dining room’s recent expansion. Let the crowds come. There’s lots to explore.