PCBgogo

“There is no RS232 connector on the oven, although the controller board seems to have an unused connector with two optocouplers that looks suspiciously like an isolated serial communication interface.” Having recently received one of these myself, I decided to go straight for the COM port to see what's going on, as it would be nice to at least have some temperature readouts. The board itself uses a CY96610 Series CY96F613 microcontroller ,To get the ball rolling, I have reverse engineered the "COM" port connection.
Unfortunately connecting to either the TX output or R25 to a scope doesn't output any data when the unit is switched on, or when sitting on the main page. The next step is to build a USB/UART adapter to power up the RX optocoupler and try sending commands to it.
If I cannot get anywhere with this, I might consider decoding the LCD outputs and interfacing with the buttons to control it. The LCD is a standard 128x64 dot matrix LCD with model number 12864D1 V3.0, and the buttons wired to a separate board. There's no markings on the other side of the LCD PCB.
Stay tuned!Edit:
Looking at the Cypress datasheet, header W1 is connected to DEBUG I/F with a pullup which is the one wire debug interface. When the DEBUG I/F and MD pins are held low on reset (MD is tied to ground and the other side of W1 is ground), it enables serial programming on USART2 (and USART7,USART8). According to the datasheet, USART2 uses SIN2-Pin7 SOT2-Pin8 and SCK2-Pin9 for programming, however on this board the SCK2 pin is used elsewhere, so I'm pretty sure the COM header isn't used for serial programming, as you'd expect SCK2 to also be connected through (this alleviates some doubt I had about it possibly being just a programming interface).
Edit 2:
I connected this up to a USB->UART adapter and cycled through all possible serial speeds and settings. Unfortunately there is no response even though the signal gets through the optocoupler (although it's inverted on the output compared to the TX pin, so it might need something else). Considering this board has a 420 label on the speaker sticker, I'm guessing this board is a generic controller, with custom firmware depending on the board.
Edit 3:
Reading further into the technical reference manual, the third USART connection for SCLK is actually not required for serial programming. So it could very well be that this COM port is in fact a flash programming connector...  
Edit 4: 
I'm not really willing to mess with the DEBUG I/F and put this into serial programming mode, in case I brick the firmware. Instead I'm going to create an adapter to interface with the LCD and decode the menu from that information.
Edit 5: 

After hooking up a logic analyser to the display, I can confirm that it is infact a KS0108 with the same interface/pinout as the vishay display linked above (it seems most of these LCDs follow the same pinout order at least for the data pins).