Preheat oven to 400 degrees.
Cut zucchinis in half lengthwise, use a tablespoon to scoop out the seedy centers and discard. Place zucchinis side by side, cut side up, on a baking sheet or in a casserole dish.
In a large skillet brown the ground beef, stirring frequently, for 5-6 minutes. Add onions, rice, diced tomatoes and green chiles, cumin, chili powder, garlic powder, salt and pepper. Stir and simmer for 3-5 minutes.
Spoon ground beef and rice mixture into prepared zucchinis. Bake for 15 minutes.
Top zucchinis with cheeses and return to oven for 5 minutes until melted.
Garnish with your favorite toppings like cilantro, sour cream, tomatoes, olives, avocados, and serve.