Blanch beans: Drop into a pot of heavily salted boiling water (it should taste like seawater). Cook until tender-crisp and bright green, 2 to 3 minutes, then drain and drop into ice water until cool. Drain and set aside.
Meanwhile, in a small bowl, whisk together oil, kimchi juice, salt, chili paste, and vinegar to taste.
Drain beans, pat dry, and put in a large bowl along with chopped kimchi, chicken, tomatoes, and cilantro. Gently toss with enough dressing to coat. Serve any remaining dressing on the side.
*Find kimchi with refrigerated foods at well-stocked grocery stores. Find gochujang at Asian markets and online.