Salt the cucumbers. Trim the cucumbers, then smash them with the side of a large knife, rolling pin, or the bottom of a sturdy measuring cup until they crack open. Roughly chop them into bite-size pieces and place them in a fine-mesh strainer set over a bowl. Season with two pinches of salt and toss well. Let the cucumbers sit while you prepare the rest of the recipe.
Make the panko sesame-crunch. Heat a large skillet over medium heat. Add panko and sesame seeds and cook, stirring often, until the panko turns deeply golden and the sesame seeds smell nutty, 5 to 8 minutes. Lower the heat if the crumbs start browning too quickly.Transfer the mixture to a plate or shallow bowl. While still warm, stir in the gochugaru, zest of 1 lime, and a pinch of salt. Set aside to cool. Make the dressing. In a large bowl, whisk together the kimchi paste or gochujang (See, Note 1), rice vinegar, lime juice, sesame oil, tamari, and fish sauce until smooth and glossy. Taste and season with more tamari or lime juice.
Make the kimchi sauce. In a medium bowl, stir together the labneh or Greek yogurt and kimchi paste or gochujang until smooth. Taste and adjust with lime juice if you want it tangier.
Finish the salad. Gently shake the cucumbers to drain off any excess liquid, then pat them dry with paper towels. Add them to the bowl with the dressing, along with the drained tuna, chopped kimchi, carrots, scallions, and cilantro.Fold gently to coat everything without breaking up the tuna too much. Add the baby greens and about half of the panko-sesame crunch, then fold again just until the greens are lightly dressed. Plate and serve. Spread a generous swoosh of kimchi sauce onto each plate. Pile the salad over top, then finish with more panko-sesame crunch and a squeeze of fresh lime.
