Place beef pieces into a bowl and add salt, black pepper, cayenne pepper, and paprika. Toss very thoroughly until meat is evenly coated. Let sit at room temperature for about 20 minutes before browning, or place in the fridge until needed.

Add oil to a heavy-bottomed pot, and heat on high until oil is shimmering. Add beef in a single layer, and sear until a nice brown crust forms, 3 to 5 minutes.

Turn beef over, and let other side cook about 2 minutes. Turn heat down to medium-high; remove beef to a bowl and set aside.

Add onions, celery, peppers, and minced garlic to the pot, and cook, stirring, until onions begin to turn translucent, 3 to 5 minutes.

Add beef back in along with any accumulated juices. Add soy sauce, Worcestershire sauce, granulated garlic, water, and bouillon paste. Stir and bring soup to a simmer. Lower heat to medium-low and let simmer until the meat is very tender, 60 to 90 minutes.

Taste and adjust seasoning with more salt or soy sauce as needed. Keep the soup warm on low heat until ready to serve.

Bring a large pot of lightly salted water to a boil. Cook spaghetti in boiling water, stirring occasionally, until tender, about 12 minutes. Drain and divide equally among 4 bowls.