Preheat oven to 375°F. Turn a 12-cup muffin tin upside down. Place 6 tortillas in the space between the cups to form a “bowl”. Bake for 10 to 15 minutes until firm and beginning to brown. Transfer to a cooling rack.
Cook rice according to package directions. While the rice is still warm, transfer to a large bowl. Mix in black beans, corn, tomatoes and 2 tbsp cheese.
Fill the taco shells with the rice mixture and top with cheese. Garnish with the extra toppings, if desired.