
Preheat oven to 375°F. Coat a 9-inch pie pan with cooking spray and line with the crust. Set the pan on a baking sheet.
Whisk the eggs, milk, Greek yogurt, pepper, and ¼ teaspoon salt in a medium bowl. Set aside.
Heat the oil in a medium skillet over medium-high heat. Add the onions and cook, stirring often, about 2 minutes, until translucent (this is a quick sauté, not a caramelize).
Add the shrimp and the remaining ⅛ teaspoon salt. Cook 2-3 minutes, stirring frequently, until just opaque. Remove from heat right away to avoid overcooking.
Squeeze excess water from the spinach, or sauté it 1 minute and let it cool slightly.
Spread the shrimp and onion mixture in the crust. Layer with spinach, then cheese. Pour the egg mixture on top, making sure it reaches the edges. Top with sliced tomatoes.
Bake 45-50 minutes, until puffed and firm in the center. Tent with foil if the crust browns too fast.
Cool on a wire rack for 15 minutes before slicing into 6 pieces.