Season chops with 1/4 tsp thyme, salt and pepper (both sides).
Heat oil in a medium skillet over medium-high heat; add chops and brown well on one side before turning over to brown the other side.
After turning, scatter onion in skillet around the pork, and stirring them to coat with the oil.
Once the chops are thoroughly browned, reduce heat to medium-low; add orange juice, water, and remaining 1/2 tsp thyme to the skillet.
Bring to a simmer and cover, cooking at a slow simmer for 15 minutes (if you find that your liquid is reducing too quickly, adjust your temperature a bit downward, and add an additional tablespoon water if needed).
Meanwhile, combine sour cream (or yogurt) with the mustard in a small bowl and set aside.
After the 15 minutes simmer time, remove the cover from the skillet and continue simmering until most but not all of the liquid has evaporated (about 5 minutes).
Remove the chops (but not the onions) to serving dishes and remove the skillet from the heat.
Stir the sour cream/mustard mixture in to the skillet; reduce heat to very low and return to stove.
Heat just until the sauce is warmed, stirring all the while and never allowing to boil (just a minute or so).