In a large pot combine split peas with 8 cups of water. Bring to a boil over medium high heat and boil for 3 minutes. Turn off heat and set aside for 1 hour. Drain and rinse. Set aside.
In a skillet over medium heat heat the oil and then add the vegetables (onions - carrots), cooking for 6-10 minutes or until vegetables are softened. Add garlic, oregano and pepper and cook for another minute, stirring. Transfer to crockpot.
Stir in reserved split peas and broth.
Cover and cook on low for 8-10 hours (or on high for 4-5 hours) or until peas are tender. Add salt if needed.
Puree with and immersion blender if desired.
To make the optional persillade: in a small bowl combine persillade ingredients (or use a mini chopper). Set aside at room temperature for 30 minutes.
To serve ladle soup into individual bowls and garnish with the persillade.