In a large nonstick skillet, heat 2 tablespoons oil until shimmering. Add the onion and mushrooms and cook, stirring over high heat for about 5 minutes, until the onion has become translucent. Add the zucchini and peppers and cook, stirring, for 2 minutes more. Remove the vegetables to a dish and cover to keep warm.
Heat the remaining tablespoon of olive oil in the pan. Add the shrimp, and season to taste with the herbed seasoning mix. Cook, stirring frequently until the shrimp is pink and cooked through.
Add the vegetables back to the pan to warm. Squeeze some lemon juice over all and serve.
Store leftovers in a covered container for up to 4 days.