Soak the zucchini for at least 20 minutes in a basin of cold water and clean. After slicing away their ends, cut them lengthwise in half, then into long, thin sticks, ½inch wide or less.
Snap both ends off the green beans, then soak in a basin of cold water until ready to cook them.
Split the pepper in half, scoop away the pith-like core and seeds, skin it raw with a swiveling-blade peeler, then cut it lengthwise into ½-inch-wide strips.
If using raw tomatoes, wash them in cold water, skin raw with a swiveling-blade peeler, split them in half, scoop out the seeds without squeezing the tomato, and cut them up in small pieces.
Put the olive oil and garlic in a 12-inch sauté pan, turn on the heat to medium, and cook the garlic, stirring from time to time, until it becomes colored a very, very pale gold.
Retrieve the green beans from their soak, add them to the pan with a sprinkling of salt, then put a lid on and turn the heat down to low.
When the beans have cooked for 5 minutes, add the strips of pepper, turn, put the lid back on, and cook for another 5 minutes.
Add the zucchini, the tomatoes, and several grindings of pepper; turn over all ingredients to coat them well; and cook, uncovered, at a steady simmer, turning occasionally, for 15 or 20 minutes. Taste for doneness—the beans should be firm but tender, and the pepper and some of the zucchini will have partly dissolved. Taste and correct for salt.