Preheat your oven to 400°F (200°C). Pierce sweet potatoes with a fork and bake on a tray for 45-50 minutes until tender.
While potatoes bake, melt butter in a skillet over medium heat. Add garlic and sauté for 1 minute.
Add mushrooms, cooking until softened, about 5 minutes. Stir in spinach and cook until wilted, about 2 minutes. Season with salt, pepper, and lemon juice.
Slice the baked sweet potatoes lengthwise, scoop out a bit of the flesh to create a hollow, and stuff with the mushroom-spinach mixture.