Spicy Ramen Noodle Bowls

Name: Spicy Ramen Noodle Bowls
Ingredients: 1 tbsp canola oil; 1 bunch scallions, divided; 1 L chicken or vegetable stock, no salt added; 1 thumb sized piece of ginger, peeled and roughly chopped; 3 cloves garlic, peeled and sliced lengthwise; 1 4 piece lemongrass; 1 chili pepper, sliced lengthwise, seeds and veins removed; Juice of 1 lemon; 2 tsp fish sauce (if desired); Kosher salt