Place chicken in a shallow 2-quart microwave-safe dish with a lid; season with salt and pepper. Cover, and microwave on high until opaque throughout, 10 to 12 minutes, turning chicken halfway through. Let cool briefly; slice crosswise.
In a serving bowl, whisk vinegar, oil, mustard, Stevia, and curry powder; season with salt and pepper. Add spinach, shallots, and oranges, and toss.
4 boneless (5 oz each), skinless chicken breast halves
Coarse salt and ground pepper
1/4 cup rice vinegar
2 teaspoons olive oil
2 teaspoons yellow mustard
1/2 packet Stevia
2 teaspoons curry powder
10 ounces baby spinach
2 shallots, halved and thinly sliced
1/2 cup oranges