Wipe out the skillet. Add the 2 tablespoons of olive oil and heat until shimmering. Add the onion and bell pepper and cook over moderately high heat, stirring occasionally, until softened and just beginning to brown, about 8 minutes. Add the garlic and cook, stirring, until fragrant, about 1 minute. Add the broccoli rabe, beans, stock and olives and simmer over moderate heat for 5 minutes. Season with salt and pepper.