Place the cubed potatoes in a pot of salted water. Bring to a boil and cook until fork-tender, about 15-20 minutes. Drain and let them cool slightly.
In a skillet, heat the olive oil over medium heat. Add the chopped onion and sauté until translucent.
Stir in the minced garlic, ground cumin, and chili powder, and cook for another minute until fragrant.
Add the cooked potatoes to the skillet and mash them gently with a fork or a potato masher, creating a chunky mixture. Season with salt and pepper to taste. Cook for another 5 minutes, allowing flavors to meld together.
While the filling cooks, heat the corn tortillas in a separate skillet over medium heat for about 30 seconds on each side or until they’re warm and pliable.
Spoon the potato filling into each warm tortilla.
Top with fresh cilantro and avocado slices if desired. Serve with salsa on the side for added flavor.