Preheat oven to 325°F.
Sprinkle the oxtails with salt and pepper and dust them in flour. In a heavy-bottom pan or Dutch oven over medium heat, place oxtails in a single layer without overcrowding the pan. Sear oxtails on all sides. Repeat in batches if necessary until you have browned all the oxtails.
Add the bone broth, onion, garlic, Ro-tel tomatoes and spices. Reduce heat to low, cover and cook for 6 hours (or 6–8 hours in a slow-cooker).
With a slotted spoon, remove the meat and set aside. Strain the broth, then de-fat by placing the strained liquid in the refrigerator or freezer; the fat will rise and solidify. Remove the fat and reserve it for later use. Return the broth (minus the fat) to a pot and reduce until by half for sauce. Set sauce aside.
Melt some of the reserved fat in a pan over medium-high heat and sauté the mushrooms until cooked and tender. In a separate pan, heat olive oil on medium heat and quickly cook the baby bok choy until tender, about 10–15 minutes. Keep warm.
Boil salted water in a large pot and cook the pasta, al dente. Drain and keep warm.
Heat the cooked oxtails in the reduced sauce. Taste and adjust seasonings.
On a serving plate or large serving bowl, place cooked pasta in the center. Top with oxtail meat and sauce. Top with cooked mushrooms and lay cooked bok choy around the edges.