Heat olive oil in a large skillet over medium heat and sauté diced onion for 3 to 4 minutes until softened.
Add sliced turkey sausage and cook for 5 to 7 minutes until browned and cooked through, stirring occasionally.
Stir in minced garlic and cook for about 1 minute until fragrant.
Add frozen pierogi to the skillet, stirring carefully to combine with sausage and onions; cook 5 to 7 minutes until heated through and lightly browned.
Reduce heat to low, add fresh spinach, and cook until wilted, about 2 minutes.
Pour in heavy cream and sour cream; stir to combine. Add dried dill, salt, and pepper to taste.
Simmer mixture for 3 to 4 minutes until slightly thickened.
If desired, stir in grated Parmesan cheese for extra creaminess, then remove from heat.
Serve in a shallow bowl garnished with chopped parsley and extra Parmesan if preferred.