Heat oil in a medium pan over medium heat.
Add sliced shiitake mushrooms and sauté for 2–3 minutes until slightly golden.
Stir in minced garlic and cook until fragrant, about 30 seconds.
Reduce heat to low, add the tomato chunks, and cook for 5–7 minutes until they start breaking down into a sauce.
Stir in broth, soy sauce, oyster sauce, tomato paste, sugar, and MSG/salt. Mix well and bring to a gentle boil.
Add your chosen vegetables and cook until just tender.
Add beef slices and udon noodles. Simmer for 2–3 minutes until beef is cooked through and noodles are heated.
Ladle into bowls and enjoy immediately. Optionally, garnish with chopped green onions.