Just send the serial commands to/from ESP8266 as in arduinos's examples.
I often use PIC MCU's...sure there is the esp8266 asynchronous UART Rx Tx but the esp8266 also has synchronous I2c and SPI which often times is the superior interface to use for high speed short distances of less than a meter plus they are busses allowing more than one device via device selection.
UART is at 3.3v levels which limits distance a full 12v RS232 interface will go 400m at 40v maybe 1km or more.