Preheat oven to 400°F (200°C). Wash potatoes, pierce with a fork, rub with olive oil, salt, and pepper. Bake for 60-75 minutes until tender.
In a skillet over medium-high heat, brown ground beef. Drain excess grease. Add chopped onion and sauté until softened. Stir in diced tomatoes and taco seasoning; simmer for 5-7 minutes.
Once potatoes are cool enough to handle, cut in half lengthwise and scoop out some flesh. Mix scooped potato into taco filling. Spoon mixture back into potato halves and top with cheeses.
Bake for another 10-15 minutes until cheese is melted and bubbly.