Heat the olive oil in a pan over a medium heat and add the flour. Stir to combine until the flour forms a smooth ball (add a little more flour if necessary).
Slowly stir in the oat milk, a little at a time, stirring continuously until the sauce is smooth.
Combine a little of the oat milk with the miso paste until it's smooth and runny and add that to the sauce. Season with white pepper.
Substitute this sauce for béchamel in traditional lasagna recipes.