Tear challah into ¼-inch pieces, and place in a large bowl. Whisk together eggs, bananas, milk, sugar, cinnamon, nutmeg, vanilla, and salt in a separate large bowl. Add challah pieces, stirring until well combined. Cover with plastic wrap, and refrigerate until bread soaks up all liquid and combines with banana, 10 to 20 minutes.

While oil is heating, stir fritter mixture well until ingredients are thoroughly combined. For each Fritter, roll about 1 tablespoon of batter into a ball using your hands. Press firmly together; roll again, squeezing into a firm ball, about 1 inch in diameter. Transfer to 2 large baking sheets.

Pour oil into a 10-inch-wide Dutch oven or heavy pot; heat over medium-high to 350°F. Line a large baking sheet using paper towels.

Using a spider, place dough balls in hot oil. Fry 8 at a time, being careful not to overcrowd Dutch oven, until bottoms of Fritters are dark golden brown, about 2 minutes total, flipping Fritters halfway through frying time using a slotted metal spoon or tongs. (Adjust heat as needed to maintain temperature and prevent burning.) Transfer Fritters to prepared baking sheet. Let oil return to temperature between batches. (If desired, keep Fritters warm in a 250°F oven on an ungreased baking sheet.)

Transfer Sauce to a dish, and drizzle with silan (if using). If desired, sprinkle Fritters with powdered sugar or cinnamon sugar; serve with Sauce and, if desired, warm chocolate sauce.

Whisk together tahini, agave (as needed), lemon juice, and salt in a medium bowl until very smooth (mixture will seize up but loosen as you continue to stir). Whisk in water, 1 tablespoon at a time as needed, until Sauce is thick but pourable; set aside.