Preheat oven at 400°F.
In a medium bowl, mix the hash browns with 3 tablespoons of the olive oil, chopped green onions, the zest from half a lemon, kosher salt and fresh ground black pepper. With a spatula gently stir the potatoes thoroughly.
Brush olive oil in the interior of a non-stick 12 cup-muffin tin or use a muffin stone bakeware. Carefully mold the hash browns in each muffin cup, pressing the sides and forming a small well in the center. Bake for 20 minutes, until they start to brown lightly. Remove from oven and set aside.
Place spinach in a colander to drain water out and sauté in remaining 1 tbsp of olive oil and garlic, until most of the liquid has evaporated, about 5-6 minutes. Season with kosher salt and black pepper. Set aside to cool.
In a medium size bowl, beat the eggs and milk with a pinch of salt. Add the Boursin and goat cheese, mix well until smooth and creamy. With a spatula fold in sautéed spinach and garlic and incorporate completely.
Using a spoon, fill the potato cups with the spinach/egg mixture and bake for 15 minutes. Let cool slightly before carefully unmolding the nests.