Add the beans and water to a large saucepan over medium-high heat and bring to a boil.
Reduce the heat to medium-low then cover the pan and simmer the beans until tender, about 1 hour.
Drain and rinse the beans under cold water then transfer the beans to a large mixing bowl.
Stir the tomatoes, bell pepper, and onion in with the beans.
In a small bowl whisk together the olive oil, garlic, vinegar, 1/2 tsp salt, and 1/4 tsp black pepper until well combined then drizzle over the bean salad.
Toss the salad to coat in the dressing then taste and season with salt & pepper if needed.