In a small food processor, combine all of the mushroom butter ingredients and pulse until they combine into a smooth paste. This is your mushroom butter. Set aside on the bench until step 3.
To make the kiev, slice the breast, lengthwise, in two equal sized halves. Using a smaller knife cut a little pocket sideways (trying to not cut through the chicken) as deep as you can into each half.
In the pocket, place a large tbsp of the mushroom butter and flatten with your hand trying to spread internally as much as possible. Keep the pocket closed using the butter as glue, then season the breast carefully with salt, pepper and paprika.
Use the 1,2,3 breading technique: plate one with 1 cup of flour, plate two with 2 cups of panko and plate three with 3 eggs.
Dredge the breast first in the flour, shaking off any excess, then dip into the eggs. Drip any excess onto a plate and then dunk the breast into the breadcrumbs, squeezing the panko against the breast and making sure it is fully covered and perfectly coated.
In a large frying pan, add enough olive oil to shallow fry the chicken. Cook in separate batches three at a time, 3 minutes per side till golden brown. Allow the chicken to rest on a paper towel for 2 minutes before serving.