Preheat the oven to 375°F (190°C).
In a mixing bowl, combine the cooked brown rice, egg, Parmesan cheese, salt, and black pepper. Mix until well combined.
Press the rice mixture into the bottom and up the sides of a 9-inch tart pan to form the crust. Bake for 15 minutes until slightly firm.
While the crust is baking, prepare the filling. In a separate bowl, toss the sliced tomatoes with olive oil, balsamic vinegar, garlic powder, and half of the chopped basil.
Remove the crust from the oven and layer the tomato mixture evenly over the crust. Sprinkle the shredded mozzarella cheese on top.
Return the tart to the oven and bake for an additional 25-30 minutes, or until the cheese is melted and bubbly.
Once baked, remove from the oven and let cool for 5 minutes. Garnish with the remaining basil before slicing and serving.