Mash the plantains in a large bowl with a potato masher until slightly chunky. Add the cornmeal, buttermilk, flour, butter, scallions, onion, ginger and salt and mash and stir with the potato masher until combined but still slightly chunky. Cover the bowl and refrigerate for 30 minutes.
Line a baking sheet with paper towels. Put a large nonstick griddle or skillet over medium-high heat; brush with some of the canola oil. Ladle 1/2 cup of the plantain batter onto the griddle and spread it into a 4 1/2-inch circle. Make as many pancakes as you can, leaving some space between each. Griddle the pancakes until golden brown, about 3 minutes per side. Transfer to the baking sheet to drain any excess oil. Repeat with the remaining canola oil and batter until all the batter is used. Serve hot.