Yes, muesli is in the scrabble dictionary

...and is worth 11 points by itself if you played it.

Muesli Definition

noun

A mixture of usually untoasted rolled oats and dried fruit, often used as a breakfast cereal.
A breakfast cereal of Swiss origin consisting of rolled oats, nuts, and fruit.
A mixture of oats and other cereals, dried fruit, and nuts, eaten with milk at breakfast.