For the batter: In a small food processor, add the scallions, garlic, zest and 2 teaspoons salt. Blitz until the scallions are chopped finely, scraping down the sides as needed. Add the eggs and blitz again. Pour everything into a large bowl and add the milk. Gradually whisk in the flour to make a thick, tight batter. Add more flour by the spoonful until the proper texture is met (this should feel like it won't drip through a colander, but can be pressed through and remain stringy, not doughy).
Fill a double boiler halfway with water and add a pinch of salt. Bring to a boil and place a colander over the pot. Add a heaping cup of spaetzle batter at a time to the colander and, with a rubber or wooden spatula, press the batter through the holes into the boiling water. Be sure to scrape the bottom of the colander between pressings and stir the spaetzle into the water so the next group of batter doesn't stick to the one before it. The spaetzle is cooked when it floats to the top. Remove with a fine-mesh sieve and jiggle to remove as much water as possible.
For the pan: You may need to do this in 2 batches; if so, only add half the ingredients each time. In a large pan on medium-high heat, add the butter and oil. Add the spaetzle and saute until it builds a golden crust, then toss and cook until it's mostly golden all over but still tender, 2 to 4 minutes total. Add the chopped scallions, lemon juice and a few grinds of black pepper and toss. Serve warm.