Heat the olive oil in a medium-sized skillet over medium high heat. Add the sliced onion and saute, stirring occasionally, until onion begins to turn translucent. Reduce the heat to medium-low and continue cooking, stirring occasionally, until onion has caramelized, about 40 to 60 minutes. Note: If the onion begins drying out or sticking to the pan at any point, you can add a few tablespoons of water to de-glaze the pan. Once onion has finished caramelizing, transfer to a cutting board and chop finely.

Preheat the oven to 400 degrees F and halve and seed all of the peppers. Place the peppers in a mixing bowl and drizzle with 1 tablespoon of olive oil. Sprinkle with sea salt. 

Arrange peppers on a parchment-lined baking sheet in a single layer. Bake in the preheated oven for 8 minutes. Remove peppers from the oven and allow them to cool.

Add the cream cheese, chopped caramelized onion, garlic, Italian seasoning, and sea salt to a mixing bowl. Stir well until all ingredients are well-combined. Preheat the oven to 400 degrees F if it isn't already preheated.

Use a spoon to scoop the cream cheese mixture into the peppers. Bake in the oven another 8 to 10 minutes, or until the cream cheese is golden-brown.

Top the stuffed peppers with any additional toppings, such as chopped green onion, red pepper flakes, cheddar cheese, and/or a dollop of sour cream.