Mix the salsa, mustard and lime juice in a large bowl or ziploc bag.
Add the chicken, turning to coat with the marinade. Let it marinate in refrigerator at least 30 minutes.
Melt butter in a large skillet over medium heat until foamy.
Drain chicken saving the marinade. Add chicken to skillet in a single layer. Cook 10-15 minutes till the chicken is a light brown on both sides. Add the reserved marinade to skillet and cook 5-10 minutes or until chicken is done.
Remove chicken to a serving platter; keep warm. Boil marinade in skillet over high heat 1 minutes; pour over chicken. Top with sour cream and chopped green onions.