1. Whisk together sour cream, mayonnaise, mustard, molasses, vinegar and salt in medium-size bowl until well blended. Cover dressing and refrigerate.
2. Toss together pork cubes and barbecue sauce in medium-size bowl. Coat large 12-inch nonstick stove grill pan or heavy regular skillet with nonstick cooking spray. Heat over medium-high. Add pork; cook, turning, until cooked through and internal temperature registers 160 degrees F on instant-read thermometer, about 6 minutes. Remove to large clean bowl to cool.
3. Cook pasta in large pot of lightly salted boiling water until firm but tender, 12 minutes. Drain; add to pork in bowl. Add peppers, onion and 1 cup dressing; toss. Cover; chill.
4. To serve, pour remaining dressing over pasta; mix. Spoon pasta over a bed of fresh spinach leaves or other greens, if desired.