In a 1-qt. microwave-safe casserole,, mash the beans with a fork.
Stir in the salsa, chili powder, cumin, and salt, if desired. Stir to mix well. Stir in the cheese.
Cover with the casserole lid, and microwave on high power for 3 to 4 minutes until heated through. Remove from the microwave. Stir to mix in the melted cheese. Spread the sour cream on top. Sprinkle with the chives.
Serve warm with tortilla chips (can use fat-free chips). Cover and refrigerate leftovers, which will keep 4 to 5 days.