Preheat your available oven to 350°F as you prepare the dish.
Slice the spaghetti squash in the middle to make two pieces. Microwave for 3 minutes just to soften.
Discard the seeds with a fork or your bare hands.
Prepare a covered container and arrange the squash in. Leave to bake in the preheated oven for 45 minutes. Once the squash becomes tender, remove and put aside.
Start making the filling by heating olive oil in a skillet. Sauté the spinach and garlic in the oil.
Gently mix in the parmesan cheese, sour cream, and cream cheese in the sautéed spinach and garlic. Stir the ingredients to combine.
Transfer the filling into the empty squash halves. Distribute evenly between the two pieces. Mix with a spoon just to incorporate well. Sprinkle some mozzarella cheese on top.
Bake again for an additional 10 minutes up till the cheese is golden brown in color and melted.