For the Bò Một Nắng: Heat a dehydrator to 125°F. Using a mortar and pestle, pound lemongrass until flossy. Add chopped chiles. Pound until a paste forms. Transfer to a small bowl with fish sauce, salt, and MSG. Generously chop mixture on both sides of the portioned steak. Dehydrate 6 hours. Store in refrigerator for up to 7 days.
For the Muối Kiến: Heat oven to 350°F. On a sheet tray, combine all the ingredients. Lightly roast in oven until ants have dried. Set aside.
To Assemble and Serve: Prepare and heat a grill. Grill Bò Một Nắng until warmed through. Slice Bò Một Nắng along the grain and transfer to a serving plate. Arrange Muối Kiến alongside the steak. Serve with cucumber slices and a lemon wedge.
