Heat a heavy-bottom skillet over medium heat; add olive oil and swirl around in skillet. Cook and stir onion in the hot oil until softened, 3 to 4 minutes. Add garlic, ginger, and red pepper flakes; cook and stir until garlic and ginger are slightly browned and fragrant, about 1 minute.

Stir carrots and celery into onion mixture; cook and stir for 1 minute. Add kale and cilantro; cook and stir until kale is slightly wilted, about 45 seconds. Stir lime juice, fish sauce, and lime zest into kale mixture until kale is evenly coated in lime juice.

Serve kale salad topped with cucumber, peanuts, and mint.