In a large pot, add diced potatoes with just enough water to cover them. Bring to a boil, and cook for 15-20 minutes until potatoes are tender and can be pierced with a fork. Drain and set potatoes aside.
In another pot (or the same pot, just cleaned out), add the coconut oil, onions, and garlic. Cook on low heat for 5 minutes until vegetables start to become translucent. Add the cumin seed, garam masala, cumin powder, ginger, turmeric, chili flakes, salt and black pepper. Cook for 2-3 minutes, stirring well so the onion and garlic are coated in the spice. Add the frozen spinach, water, and bring to a boil. Reduce heat to low then allow spinach to cook for 15 minutes.
Using an immersion blender, blend the spinach and onion mixture until it creamy. Add the cooked potatoes and coconut milk, and simmer for an additional 10 minutes until the saag is warmed all the way through. Taste and adjust seasonings, adding more salt, pepper, or chili flakes as desired.
Serve with basmati rice, garlic naan bread, and enjoy!