Heat 1 tablespoon oil and sliced garlic in a skillet over medium heat. When garlic begins to sizzle, remove and discard. Add rosemary to oil, and immediately pour into a heatproof bowl. Let cool.
Season tuna with 1/4 teaspoon salt and 1/8 teaspoon pepper. Rub half the rosemary oil over tuna. Let stand 15 minutes.
Heat 2 teaspoons oil in a skillet over medium-high heat until hot. Add tuna, and sear until dark golden brown, about 1 minute per side. Transfer to a plate, and cover loosely with parchment. Let rest.
Heat remaining teaspoon oil in a saucepan over medium heat. Add thyme, red-pepper flakes, and minced garlic, and cook, stirring, 1 minute. Add kale, and cook 2 minutes. Add stock, and simmer 5 minutes. Add beans and tomatoes, and simmer 2 minutes. Stir in vinegar and remaining salt and pepper.
Thinly slice tuna. Drizzle rosemary oil over tuna and beans on serving plates.