- To make the sauce : Stir together the sauce ingredients in a medium bowl. Cover and refrigerate until ready to use.
- To make the croquettes : Place the sweet potatoes in a pot and cover with water. Bring to a boil and cook for about 7 minutes, until tender. Drain well.
- Place the chickpeas and 1 tablespoon brine in a large bowl and mash until broken into small pieces. Add the sweet potatoes and mash until mostly smooth. Add the green onions, cornmeal, garlic, lemon zest, paprika, cayenne pepper, salt, and pepper.
- Stir until combined. Line a baking sheet with parchment paper or a silicone baking mat. Pour the bread crumbs into a shallow bowl.
- Scoop up an amount of the croquette mixture slightly larger than a golf ball, shape it into a patty, coat it in bread crumbs, and place it on the prepared baking sheet. Repeat with the remaining croquette mixture.
- Line a plate with paper towels. Heat a large frying pan, preferably cast iron, over medium heat. Add enough olive oil to coat the bottom of the pan and let it heat until it shimmers.
- Add half of the croquettes and cook for 3 to 4 minutes on each side, until golden. Transfer to the plate to drain. Add more oil to the pan if needed (allow the oil to heat if you add more).
- Cook the remaining croquettes. Serve warm with the dill yogurt sauce. Leftovers will keep in airtight containers in the fridge for 2 to 3 days.