Prepare the ingredients: crush and finely chop 5 garlic cloves, and thinly slice 2-3 green onions, keeping the white and green parts separate.
2
Make the sauce: mix together 3 Tbsp miso, 1 Tbsp oyster sauce, 1 tsp chicken bouillon powder, and 1 Tbsp mirin in a small bowl.
3
Cook the pasta: bring a pot of water to a boil, add 2 servings of spaghetti noodles, and cook until al dente, then drain.
4
Make the butter sauce: melt 4 Tbsp unsalted butter in a large pan over medium-high heat, add the chopped garlic and white parts of green onions, and sauté for about 1 minute until the garlic turns golden brown.
5
Reduce heat to low, add the prepared sauce, and stir for about 1 minute to deepen the miso flavors.
6
Add 1/2 cup pasta water, stir well, and simmer for about 1 minute until everything is fully combined.
7
Add the cooked noodles to the sauce, stir in 1/4 cup Parmigiano-Reggiano and black pepper, and toss everything together well.
8
Plate and serve: transfer the noodles to a serving plate, garnish with julienne cucumber and green onion tops, and optionally serve with lemon wedge or chili oil.