Place a small slit in the side of each chicken breast, being careful not to cut all the way through. Make enough space to fit a couple of spoonfuls of filling.
Mix together the cheese, mushrooms, shallots, butter and garlic in a small bowl. Stuff a couple of spoonfuls into each chicken breast and close with a toothpick.
Place the chicken breast in a single layer in the crockpot.
Pour the chicken broth in the bottom - just enough so that the top half of the chicken is exposed.
Brush olive oil over the top of the chicken and sprinkle with salt, pepper and thyme.
Cover and cook on high for 4 hours.
Notes
I haven't tried cooking these on low for a longer cooking time, but I think it would work. The chicken may not get as brown and crispy on the top but would still have great flavor.