Add the olive oil to a large pan and heat over medium-high heat.
Add the onions, sea salt, and pepper, and cook, stirring frequently, over medium heat until the onions caramelize into a deep brown color (approx. 12-15 min.).
If the onions are browning too quickly, you can turn down the heat and add a little water.
When the onions are done, add the minced garlic, and apple cider vinegar, and stir for 1 minute until the garlic is fragrant.
Remove from heat, and allow to cool.
In a mixing bowl, combine the cooled onions, fresh thyme, and the greek yogurt, and stir until blended.
Season with additional sea salt and/or pepper, to taste.
Refrigerate until chilled. Serve with sliced bell peppers, carrot sticks, celery sticks, or sweet potato chips.