Finely grind oats in blender. Whisk with flour, baking powder, cinnamon, and salt.
Separately whisk bananas, eggs, milk, vanilla, and 1 tablespoon oil. Fold into dry mixture; stand 5 minutes.
Heat nonstick griddle over medium; lightly brush with some remaining oil. Cook 1/4 cup batter per pancake 2 to 3 minutes until bubbly with set edges. Flip; cook 1 to 2 minutes until centers fully set. Make about 12 in batches.
Briefly rack-cool cooked pancakes; refrigerate within 2 hours and chill fully. Stack with parchment between; bag, label, and freeze up to 2 months.
Put 3 frozen pancakes on microwave-safe plate; cover with damp paper towel. Microwave 45 seconds, turn, then heat in 20-second bursts to 165°F in centers.
If desired, crisp warm pancakes in dry skillet over medium about 30 seconds per side. Serve 3 per portion with 1 tablespoon maple syrup.