Get the bell peppers ready by removing the tops and seeds. Put them to the side, and reserve the tops.
In a large skillet, heat the olive oil over medium-high heat; add the diced onions and cook for 2 minutes or until translucent.
Stir in the garlic and continue to cook for 20 seconds or until fragrant.
Add the ground pork to the skillet and break it up with a spatula or wooden spoon while it cooks.
Season with salt, pepper, and thyme; stir and continue to cook until browned on all sides, about 5 to 7 minutes. Carefully drain and discard the grease.
Return the skillet to the burner and mix in the tomato paste. Stir in the diced tomatoes and rice; cook for 2 more minutes or just until heated through.
Remove from heat and stuff each bell pepper with the ground pork mixture.
Arrange the stuffed bell peppers inside the insert of the crock pot.
Place the reserved tops back onto each bell pepper.
Pour water around the base of the peppers.
Cover and cook on LOW for 6 to 7 hours or on HIGH for about 4 hours.
Remove and serve the peppers topped with a dollop of yogurt or sour cream.