How to Make It
Heat 1 tablespoon of the oil in a large skillet over high heat. Add the mushrooms and ¼ teaspoon salt and cook, stirring occasionally, until brown and some liquid is released, 5 to 7 minutes. Transfer the mushrooms and liquid to a medium bowl; reserve the skillet.
Add 1 tablespoon of the remaining oil to the skillet. Add the zucchini and ¼ teaspoon salt and cook, tossing once, until brown and crisp-tender, 3 to 4 minutes. Transfer to the bowl with the mushrooms; reserve the skillet.
Add the remaining tablespoon of oil to the skillet. Add the onion, reduce heat to medium-high, and cook, stirring occasionally, until golden brown, 5 to 7 minutes. Add the garlic and cook until fragrant, 30 seconds.
Add the beans, red pepper, mushrooms and zucchini, ½ teaspoon salt, and ¼ teaspoon black pepper to the skillet and cook, stirring, until the beans are warm, 1 to 2 minutes.