Set out three shallow dishes, and put the flour in one, the egg in other and the breadcrumbs in the third.
Dip the chicken pieces in the flour, shake off any excess, then dip in the egg and finally press into the bread crumbs to coat well.
Heat the oil in a heavy bottomed skillet over medium high heat and cook the chicken until browned and crispy, about 3 - 4 minutes per side.
Place the cooked chicken in the bottom of a casserole dish.
Toss the mushrooms and spinach together with the olive oil and balsamic in a bowl, then press this firmly on top of the chicken breasts.
Cook in the oven for about 10 minutes, then sprinkle over the cheese and cook for about 10 minutes more, until the cheese is melted and the spinach is wilted and cooked.
Remove and serve with rice, risotto or pasta on the side.