For the red onion jam: In a nonstick pan or heavy skillet, heat the olive oil over medium heat. Add the onion and sprinkle with salt. Stir and cook until tender and translucent, 5 to 7 minutes.
Add the water and cook until the onion is very soft and the water has cooked off, about 10 minutes more. Add the vinegar and sprinkle the onions with the sugar. Stir well and cook for 2 to 3 minutes more, until the vinegar has cooked off completely. Season with salt and set aside.
For the fritters: Preheat the oven to 375°F.
Pulse the chickpeas in a food processor fitted with the blade attachment until they form a thick paste. Transfer to a large bowl and add the onion and zucchini. Use clean hands to mix well, then form the mixture into 10 cakes; set aside.
Combine the chickpea flour and the salt on a large plate. Gently dredge each cake in the flour, patting it onto all sides of the cake.
Add enough oil to cover the bottom of a large frying pan or skillet and heat over medium-high heat until shimmering. Add 3 or 4 cakes at a time and cook until golden-brown, 2 to 3 minutes on each side. Transfer the cakes to a rimmed baking sheet. Repeat with cooking the remaining cakes, adding more oil to the pan as needed.
When all the cakes are cooked, bake until hot and a deeper golden colour, 10 to 15 minutes more. Serve hot with the red onion marmalade.