Grate the potatoes and onions into a colander. Add 2 of the eggs and combine with the grated potato mixture. Add garlic and spinach. Mix well and press out excess liquid through the colander.
Transfer the potato mixture into a large mixing bowl. Add the remaining egg, the matzo meal, salt and pepper. Combine well with your hands. If the mixture is loose, add more meal. Allow the pancake mixture to rest 5 minutes while you heat the oil in a large nonstick skillet over medium heat.
Add large spoonfuls of the pancake mixture and press down gently with the back of the spoon to form 1/2-inch thick pancakes about 3 inches in diameter.
Cook 5 minutes until golden brown, turn pancakes and repeat the process until both sides are cooked. If the pancakes are still a bit undercooked, put them on a baking sheet for an additional 5-8 minutes in a 375-degree oven.