Wash the peppers; cut the tops off and remove all the seeds. Set aside.
In a mixing bowl, combine ricotta cheese, feta cheese, parmesan cheese, green onions, garlic, thyme, parsley, salt and pepper; mix until smooth and well combined.
Using a butter knife, fill the peppers with the cheese mixture.
Heat oil in a cast iron skillet. *Use enough oil to cover the bottom of the skillet, and come-up about 1/8-inch on the sides of the skillet.
Add peppers to skillet; cook the peppers over medium-low heat, turning occasionally, until the peppers are blistered all over and the filling is piping hot and melting; about 8 to 10 minutes. Depending on the size of your skillet, you will have to cook the peppers in batches.
Remove from heat.
Transfer peppers to a serving plate.
Sprinkle peppers with salt.