Fill a large bowl with ice water. Bring a large saucepan of water to a boil. Salt the water, add the haricots verts and cook until crisp-tender, 1 to 2 minutes. Using a slotted spoon, transfer to the ice water to cool. Transfer to a cutting board. Pat dry; cut in half.
Using a small sharp knife, slice a small X into the bottom of the whole cherry tomatoes. Add to the boiling water and cook until the skin begins to peel off, 10 to 15 seconds. Using a slotted spoon, transfer to the ice water to cool (add more ice if needed). Peel off the skins and transfer to a blender. Add the vinegar and oregano; puree. Season the tomato vinaigrette to taste with salt and pepper.
In a large skillet, heat 2 tbsp. oil over low. Add the onion and garlic and cook, stirring occasionally, until the onion is translucent, about 10 minutes. Stir in the chickpeas, stock, bay leaf and crushed red pepper. Simmer, stirring occasionally, until the flavors meld, 15 to 20 minutes; season. Discard the bay leaf. Fold in the halved haricots verts and the remaining 1/2 cup halved cherry tomatoes.
In a large cast-iron or other heavy skillet, heat the remaining 2 tbsp. oil over medium-high. Season the tuna on both sides with salt and pepper. Cook until browned, turning halfway through, 2 to 3 minutes per side for medium.
In a small bowl, toss the herbs, lemon zest and juice. Divide the chickpea mixture among 4 plates. Top with the tuna, tomato vinaigrette and herb mixture.