Bring a small pot with rice and 11/2 cups water to a boil. Reduce to a simmer, cover, and cook until tender, 18-20 minutes. Remove from burner and set aside covered. While rice cooks, prepare ingredients.

Quarter mushrooms. Remove any discolored outer leaves from bok choy. Trim end and remove leaves. Cut stems into 1" lengths at an angle and coarsely chop leaves. Stem, seed, and slice red bell pepper into thin strips. Trim cucumber and cut into thin ovals on an angle.

Stir together teriyaki glaze, gochujang (to taste), and 1 Tbsp. olive oil in a large mixing bowl. Add mushrooms and bok choy stems and use your hands to coat. Place vegetables on prepared baking sheet and spread into a single layer. Roast until slightly charred, 14-16 minutes. Reserve bowl and excess glaze; no need to wipe clean. While vegetables roast, make dressing.

Stir together rice wine vinegar, sugar, 1 tsp. olive oil, 1/4 tsp. salt, and a pinch of pepper in reserved mixing bowl with glaze.

When vegetables have 5 minutes left to roast, add red bell pepper, cucumber, shredded red cabbage, and bok choy leaves to bowl with dressing and toss to coat. Dressing the vegetables later will prevent them from getting soggy.

Place rice in a bowl and top with dressed vegetables. Top with roasted vegetables and serve.