Blanch the green beans: Add the cut green beans to a pot of salted, boiling water. Boil for 2 minutes, or until cooked to your desired texture, then drain and immediately cool the green beans in ice water.
Drain the green beans from the ice water, and add to a large bowl with the chickpeas and red kidney beans.
In another bowl, whisk together the dressing ingredients (olive oil, balsamic vinegar, lemon zest, lemon juice, garlic, salt, and thyme).
Add the dressing and tuna (including the tuna olive oil from the can) to the bowl with the beans. Gently toss together to evenly coat the beans.
Taste the salad for additional seasonings. Add more seasonings if needed. Chill until ready to serve.