Preheat oven to 375˚F.
Slice off 1/2 inch of the stem end of the tomatoes and hollow out the inside.
Slice just a small section off of the bottom of the tomatoes so that they will sit flat on a baking sheet.
Sprinkle salt in the hollow portion of each tomato and place hollow side up on the baking sheet. Set aside.
Place water and quinoa in a saucepan and bring to a boil; lower to a simmer, cover, and cook for 15 minutes.
Meanwhile, heat the olive oil in a frying pan and stir in the spinach; season with salt and pepper, and cook until just wilted.
Stir in the garlic and parsley, cook for a minute longer, and remove from the burner.
Add cooked quinoa to the spinach and mix well.
Taste for salt and pepper and adjust accordingly.
Evenly divide the filling among the tomatoes.
Cover with foil and bake for 20 minutes.
Remove foil, sprinkle tops with parmesan cheese and mozzarella cheese.
Bake uncovered for an additional 5 minutes or until cheese is melted.
Serve.