Bring a large pot of lightly, salted water to boil. Add linguini and cook until just tender, about 8 minutes. While this occurs, heat the oil in a large skillet over medium heat. Add the bell peppers and garlic and cook until just tender, about 3-4 minutes. Add the tuna, olives, green onions and lemon juice and zest and cook 1 minute more. When the pasta is cooked, save 1/2 cup of its cooking liquid. Drain the pasta well, and then add it and the 1/2 cup of cooking liquid to the tuna mixture, gently tossing. Season with salt and pepper and serve.