You can eat whatever you want on FDs as long as you stay under the calorie limits. Most of us find it easier to stick to a FD if we don’t eat the types of foods that tend to make use want to keep eating (eg high sugar or high salt snacks).

I regularly eat legumes on FDs and have had no issues. Because of the fibre content I find them a good source of protein that helps me feel full longer.

I have several recipes which I use for Fast Days involving chickpeas. They are nutritious, delicious, and [in the right amounts] stay under 300 calories.
The things to avoid are pastas and breads and other processed carbs. Carbs fro legumes and fruits are OK.