Heat 3 tablespoons olive oil in a deep skillet over medium heat. Add the garlic and chopped sage and cook until the garlic just starts to brown, about 4 minutes. Add the beans (including the liquid from the cans) and 1 cup water. Increase the heat to medium high and cook, stirring occasionally, until slightly reduced, about 10 minutes. Add the kale and cook, stirring occasionally, until the kale is tender and the liquid looks creamy, 8 to 10 minutes. Season with salt and pepper.
Meanwhile, toss the tomatoes, celery, olives and roasted peppers in a medium bowl. Heat the remaining 3 tablespoons olive oil in a small skillet over medium heat, then fry the sage leaves until crisp, 3 to 4 minutes; drain on paper towels. Reserve the oil.
Break the tuna into large chunks and divide among shallow bowls. Spoon the bean mixture around the tuna and top with the olive salad and fried sage. Drizzle with the reserved sage oil and season with salt.