Add water to a large saucepan and bring to a rapid boil.
Add brussels sprouts to water and cook for 10 to 12 minutes, or until desired tenderness.
In the meantime, prepare the sauce by combining sour cream, yogurt, dijon mustard, lemon juice, garlic salt, oregano, salt and pepper in a mixing bowl; stir until thoroughly incorporated. Taste for seasonings and adjust accordingly.
Drain brussels sprouts and rinse with cold water so they stop cooking; drain again.
Add brussels sprouts to dijon mixture and toss to coat.
Transfer to a serving plate.
Garnish with dried oregano, fresh cracked pepper, and lemon zest.