In a large skillet, over medium heat, heat olive oil. Once warm, add onion and season with salt. Sauté until soft and translucent, about 3 to 5 minutes.
Add garlic and sauté until fragrant, about 2 minutes. Add potatoes, mix well, and cook until fork-tender.
Gradually add spinach, stirring to combine. Cook until just wilted. Season with salt and black pepper.
Place potato mixture into tortillas. Garnish with red onion and lime wedge.