In a bowl, combine the oats, raisins, and seeds.
Place the Marshmallow Crème, butter, and milk in a large, heavy saucepan. Cook over medium heat, stirring with a heatproof spatula, until the marshmallow is mostly melted. Add the peanut butter, cinnamon and vanilla extract. When a few lumps remain, remove the pot from the heat and stir until the mixture is smooth. Dump in the oat mixture and stir until all the ingredients are well combined.
Spread the oat mixture in the prepared pan in an even layer. Moisten your hand lightly with water and press to pack it firmly. Refrigerate until the oat mixture sets. Using a sharp knife, cut the chilled oats into 3 wide strips. Cut each strip crosswise into 8 bars. Serve cold or at room temperature. These bars keep in a tightly sealed container for up to 5 days.