Soak dried shiitake in hot water for 20-30 minutes to rehydrate them. Sliced them thinly. Reserve a cup of shiitake water for later use.
Crumbled up tofu into small pieces, either by using a fork or your hands.
Cook noodles according to package instructions. Set aside.
Heat up about ½ tablespoon of neutral oil in a cast iron skillet / non-stick pan on medium high heat. Add in chunjang and fry for 2-3 minutes, stirring constantly. This helps remove the bitterness of the paste. Remove from pan and set aside.
In the same pan, heat up another ½ tablespoon of oil and add in onion. Stir-fry until onion is translucent, about 2-3 minutes. Add in garlic and cook for an additional 1-2 minutes until garlic is fragrant, stirring frequently.
Next, stir in all veggies and crumbled tofu into the pan and cook for 3-4 minutes, or until veggies have softened. Add black bean paste back to the pan and stir until the paste is evenly distributed.
Now, add in 1 cup of reserved shiitake water. Bring mixture to a boil, then lower heat to a simmer. Let it cook, uncovered for 3-4 minutes. In the meantime, make cornstarch slurry by mixing cornstarch with ¼ cup water.
Add slurry into the pan and cook until sauce has thicken. Give it a taste and season with salt, if needed. Serve it over cooked noodles and enjoy !