Coat chicken with balsamic, oil, seasoning and rosemary and set aside. In a skillet, add chopped bacon, work in 2 batches if preparing salad for 4. Brown bacon over medium high heat, then transfer the bits to a paper towel lined plate to drain. Using center cut bacon will cut down on the pan drippings that spatter.
Coarsely chop spinach leaves and add to salad bowl. Top with mushrooms, radishes, scallions. Season salad with salt and pepper.
Wipe out the bacon pan and return to stove turning heat back to medium low. Add 1 tablespoon oil for your dressing and shallots and reduce heat to medium. Saute shallots for 3 minutes. Remove oil and shallots from heat.
In a bowl, combine mustard and balsamic vinegar. Stream in 2/3 cup oil slowly while whisking the dressing to emulsify it. Add warm shallots and toss with spinach salad to coat evenly. Add cooked bacon and toss again.
Preheat a nonstick skillet over medium high heat. Cook chicken cutlets, 4 minutes on each side, in a single layer. Slice breasts on an angle on your cutting board once they are all out of the pan. Pile spinach salad on to dinner plate/plates. Top each salad with 2 sliced chicken cutlet pieces. For individual portion follow the above method.