Put the chickpeas in a medium bowl and add water to cover generously. Soak overnight.
Cook the chickpeas:
Drain the chickpeas. In a medium saucepan, heat 2 tablespoons of the canola oil over medium heat. Add the chickpeas and stir to coat them with the oil. Then cover with 5 cups of water and bring it to a boil over medium heat. Lower the heat and simmer until the chickpeas are tender but still hold their shape, 45 minutes to 1 hour. You may need to add more water to finish cooking them. Drain.
Char the onion:
Heat in a medium skillet over medium heat and add the remaining 2 tablespoons oil. When the oil begins to smoke lightly, remove the skillet from the head and add the onion and 1 teaspoon salt. Return the pan to high heat and cook, stirring from time to time, until the onion chars around the edges, 5 to 8 minutes. Remove the skillet from the heat.
Make the dressing and finish the salad: In a large bowl, whisk together the tahini, lemon juice, red wine vinegar, and coriander until smooth. If the dressing is too thick, stir in a little water. Stir in the onion, chickpeas, 1 tablespoon salt and the scallions. Taste for seasoning, and serve.