Step 1Rinse the beans under cold running water. Drain, leaving any water clinging to the beans. Trim the ends and set aside.
Step 2In a large skillet, heat 2 tablespoons of the olive oil. Add the shallots and saute over medium heat about 1 minute. Add the garlic and continue to saute for 30 to 45 seconds, until tender and fragrant but not browned. Remove the sauteed shallots and garlic from the pan with a slotted spoon, pressing any excess oil back into the skillet. Set aside.
Step 3Add the remaining 1 tablespoon oil to the skillet. Once the oil is hot, add the beans, oregano leaves, salt and pepper to taste. Saute over medium heat, stirring frequently until the beans are browned in spots and tender but retain some crispness, about 10 to 12 minutes. Stir in the tomatoes and cook 2 minutes. Stir in the sauteed shallots and garlic. Cook just until aromatic, about 30 seconds.
Step 4Remove the pan from heat and let the beans cool slightly. Stir in the balsamic vinegar and allow contents to cool to room temperature. Remove the salad from the pan to a serving platter.