Preheat oven to 375 degrees F.
Fit the pie crust into a 9-inch pie plate and prick the bottom several times with a fork. Line with parchment and fill with pie weights or dried beans. Bake for 12 minutes. Remove weights and parchment and bake 5 minutes more. Set aside to cool.
Arrange tomato slices on paper towels and sprinkle evenly with kosher salt. Let stand 20-30 minutes to draw out moisture, then pat thoroughly dry.
In a medium bowl, stir together cheddar, mozzarella, Parmesan, mayonnaise, garlic powder, and onion powder until evenly combined.
Layer half the tomato slices in the crust. Top with half the green onions, basil, parsley, and black pepper. Repeat with remaining tomatoes and herbs.
Spread the cheese mixture evenly over the top, covering the tomatoes completely.
Bake for 35-40 minutes, until the topping is golden brown and bubbling around the edges.
Rest 15-20 minutes before slicing. Garnish with fresh basil and serve warm.