You can see a proper Ayambil Oli thali photo on this page (it includes images along with explanation of the vrat and food restrictions):

Typical Ayambil Oli thali (both Shwetambar and Digambar traditions) will have:

• One-time boiled grains or pulses (e.g., rice, wheat, udad, etc.)
• No milk, curd, ghee, oil, sugar/jaggery, fruits or vegetables
• Very little or no spices, and usually no salt

The focus is on simple, almost tasteless food taken once a day, to practice tapa and control over taste.