In a large bowl, combine the cucumbers, baby greens, red onion, chili, radishes, and scallion. Toss with a drizzle of olive oil, lemon juice, and a pinch of salt.
In a small bowl, whisk together the peanut butter, hot water, soy sauce, sweet chili sauce, lemon juice, sesame oil, and salt until smooth and pourable. Add a splash of more water if needed to loosen the consistency.
Heat a skillet over high heat. Pat the tuna dry with paper towels, season with salt and pepper, and sear in the hot skillet with olive oil for about 3 minutes, turning occasionally to brown on all sides.
Add the teriyaki sauce and sesame seeds and stir to coat. Cook for another 1 to 2 minutes until glazed but still pink in the center. Remove from heat.
Arrange the salad on two plates. Top with the warm tuna cubes and drizzle generously with the peanut dressing. Serve immediately.