Preheat the oven to 350°F (180°C or 160° for a fan oven).
Grease and flour a 12 cup muffin pan or use paper liners.
Beat the oil and the eggs together in a medium bowl or jug.
Beat in the vanilla. Set aside.
In another, larger bowl, mix together the flour, chia seeds, sugar, baking powder and baking soda.
Add the oil and egg mixture to the flour mixture in the larger bowl and stir just until combined. The batter will be very thick at this stage.
Stir in the bananas and the raisins until thoroughly combined.
Divide the batter between the muffin cups. (I use an ice cream scoop for this.)
Bake for 15 to 20 minutes or until a skewer inserted in the muffins comes out clean.
Cool on a wire rack. Delicious served warm or at room temperature but don't eat them straight out of the oven as the raisins will be very hot!