1. Prepare the sweet potatoes: Preheat your oven to 400°F (200°C). Pierce each sweet potato several times with a fork. Bake them directly on the oven rack for 45-60 minutes, or until tender when squeezed.
2. Sauté the filling: While the potatoes bake, heat olive oil in a large skillet over medium heat. Add the chopped red onion and cook until softened, about 3-5 minutes. Stir in the black beans, chili powder, and cumin. Cook for another 5 minutes.
3. Combine with spinach: Add fresh spinach to the skillet. Cook until it wilts, which takes about 2-3 minutes. Season the mixture with salt and pepper to your liking.
4. Stuff the sweet potatoes: Carefully slice each baked sweet potato lengthwise, but not all the way through. Fluff the interior flesh with a fork. Spoon the savory filling into each potato.
5. Add cheese and bake: Top generously with shredded cheese. Return the stuffed sweet potatoes to the oven for 10-15 minutes, or until the cheese is melted and bubbly.
6. Garnish and serve: Garnish with fresh cilantro and a dollop of salsa, if desired. Serve your gluten-free cheese stuffed sweet potato warm. Consider pairing it with a fresh green salad for a complete meal.