First off, heat the olive oil in a medium saucepan.
Season raw chicken cubes with salt and pepper and add a few fresh thyme leaves.
Brown the chicken in the olive oil until done. Remove chicken from pan.
Deglaze the pan by adding ¼ cup of water, and then add the mushrooms, butter and the rest of the fresh thyme.
Cook the mushrooms until they lose their moisture. Remove from heat and set aside.
In a large saucepan heat the butter until melted, add the flour and whisk through.
Add half of the milk and whisk until thickened. Add the last of the milk and keep on whisking until flour cooks through and the ideal thickness of your béchamel sauce is reached.
Take off the heat and add the mustard and the rest of the dry spices.
Season with salt and pepper.
Mix the chicken, mushrooms and mustard sauce altogether and serve on fluffy rice.